agroves -- I agree with most of what has been said regarding higher scores caused by oil patterns and "old school" versus "new school" bowlers. I would like to address a different part of your original post, why it happened and who is responsible. There is a lot more on this on the PBA "past bowlers" forum under the Billy Hardwick thread that has been mentioned in other posts.
When the transition between lacquer and urethane finishes first happened in the late 60's and early 70's, the urethane finishes did not score as well because the oil did not hold up. Human nature being what it is, the bowlers migrated to those houses that were still using lacquer. Then the managers of the houses using urethane realized that to keep their business they had to do something. So they started fiddling with the oiling machines, especially the B-90's that were easy to modify, and set up a condition that scored well, called a block. And the bowlers migrated from the lacquer houses (which were becoming rare because of the danger of fire while refinishing the lacquer surfaces) back to the urethane houses. Pretty soon all the houses were blocked and any house that had competition that didn't block didn't have much business. And it is the same way today, any house that doesn't put out an easy shot loses business.
So who's to blame? To quote the famous philosopher, Pogo, "We have seen the enemy and he is us!" Stop bowling in houses with easy shots and flat oil patterns will come back. Of course, I really don't expect that to happen. -- JohnP