I don't post much lately for lack of time but I check in on topics a few times a week and this one caught my eye. I do have a good working knowledge of this subject having re-built and customized my own table to proper specifications. Hint, hint...EVERYONE complains that my table is too tight.
So my two pence worth...
There are several factors that determine how easily the pocket will accept a ball that is off line. Most obviously is the physical opening between the jaws. Everyone probably knows that there are templates for a table fitter to get the size and shape correct when putting new rubber on the cushions for instance. What everyone probably does not know is that: a) These templates are not readily available to the general public. They are the intellectual property of the WPBSA I believe and so to get access to them, then an authorized agent must be involved. and b) The templates not only set the size of the opening but also define the fall of the pocket which is probably the more important variable in determining how "generous" a pocket will play. and c) There are a couple other non-intuitive factors involved regarding the "newness" of the equipment involved that make balls slip into pockets a bit easier. These are changes in technology that I have seen happening over the course of my lifetime and though they are less obvious, this point (c) is probably the bigger reason why they appear to be "buckets" today while the actual "size" of the pocket may well be exactly the same as it was decades ago.
Most of the lifetime of my table in my ownership (a bit over 30 years), it sat in my basement, light usage, original installing fitter was a knowledgeable, very experienced, wonderful human being named Bob Graham from Canada who has since gone on to set up Snooker tables in glorious, well lit Venues for Our Maker with harp music in the background. I knew nothing about these things at that time and Bobby set my table up to his own specifications that he used for so many of the club tables around Toronto. And I enjoyed plenty of good snooker and potted plenty of balls.
About a dozen years ago, I decided to re-furbish my table and arranged my small, semi-private club. By that time, the United States Snooker Association had been organized and loaned me a set of proper templates from the WPBSA. What you should also be told is that my table is American manufactured (Brunswick-Balke-Collender) from nearly a century ago and American tables were made different than English tables. I wanted my table to replicate English standards as nearly as possible and setting the pockets to the WPBSA template made mine about the tightest table anyone had ever played before. The pocket openings were set to exactly the same as the professional standard of 2006. What I did not know at the time was that the fall of the pocket on my table was about an eighth inch deeper than the English standard. For any who don't know what the "fall of the pocket" means, it is the definition of how deep set back the hole in the slate is relative to the pocket openings. The fall of the pocket is probably the biggest difference between the pro table and the club table. Barry Stark explains it very well in that video.
Being ignorant of the importance of these things and not willing to hack up my table in an effort to make it easier to pot a ball, that is how my table stayed for about eight more years. It was tough for anyone to even break twenty. And last year, when it was time for maintenance again, one of my club members is a high end tile cutter by trade and he has all the tools needed to cleanly and accurately cut the slates. I trusted him to do the work. As an engineer, I did the mathematics to calculate exactly how much my pocket falls needed to be opened up and my tile guy did a perfect job of cutting and grinding the slate precisely. She still plays very properly tough but now I get 30's and 40's breaks pretty regularly. Half centuries still few and far between.
I recently played on a table that had recently been re-clothed with exact cloth authorized for professional tournament play, Strachan No. 10 Championship. On my table, I have the next level down, Strachan Tournament Gold, thicker and heavier. That table owner, like myself, is very exacting in his standards and so he said his pockets were also at professional standard. I found the No. 10 cloth much easier than my heavier cloth: balls rolled straighter, you could strike much gentler and the object still reaches the pocket (this makes a huge difference for the accuracy of your stroke), and because the table had been recently re-clothed (new equipment), there were shots played that seemed like they shouldn't fall but instead of rattling the jaws, they would just slip in the pocket. In that short three hours, I ran several 30's and a 40-something. And that was with being a little uncomfortable in a new venue AND having to play the game sober, which I am not so used to doing. :) To run equivalent breaks on my table back home would probably take me about 15 to 20 hours table time. Bad news about that table with the No. 10 cloth, after just six months in the field, the cloth is well worn and torn. That professional cloth is simply not meant for harsh public play.
So the upshot is that I believe the pockets are probably exactly the same size they have been for a long time (professionally), but perhaps they have opened up the fall of the pocket slightly. (For this specification, a tiny bit makes a huge difference...if they opened the fall 1/8", about every frame would be one break and done, and if they opened the fall 1/4", every frame would likely feature a century. The game would become laughably easy at the professional level.) Couple that with the fact that new, thin, tightly stretched cloth (which is always the case in any pro tournament) simply makes balls fall in pockets easier, and I believe it explains why the pockets seem to be "buckets" today.