Yes there has been some grade inflation for PCGS graded coins. I have several Morgans that were in old rattler holders that now reside in a newer NGC or PCGS holder a grade higher. When PCGS first started, they were very conservative. They had quality as the issue of utmost importance. This, along with being the first allowed them to dominate the market initially. Then with the appearance of NGC and ANACS later in the 80's, competitive forces dictated that PCGS become a little less conservative in order to hold on to their market share. This is why the original rattler holders have a higher percentage of upgrades.
However, in the last decade, this situation has stabalized where PCGS, NGC and ANACS have become very similar in their grading standards and performance. In fact, it is my opinion that NGC has been the most consistent throughout the history of graded slabs. Many have made the observation that early NGC slabs seem to be a little lower in their respective grades than the newer slabs. The answer for this is quite simple. Any coin of value that had any chance for an upgrade was resubmitted. This results in the coin being in a new holder even though the vast majority were not upgraded. As a result, a majority of coins in old NGC holders are those specimens in the middle or lower end of a grade that were not candidates for regrade.
When the top grading services are on the same page in grading, this results in the grade stability we have seen for the last 5-7 years. I don't really care what they want to call a coin as long as the "rules" remain the same. The price will move to match availability of a particular grade if the grading criteria remains stable.