It's a frustrating practice, and indeed, not limited to the Simpsons - even Doctor Who has suffered from cuts, on BBC America, of all places.

SNPP, perhaps not surprisingly, has a catalog of Simpsons syndication cuts, arranged by season:

http://www.snpp.com/episodes/scg.html

The older episodes also suffer more from that. The show lost a couple of minutes of runtime over the years, so there's more to cut. Later seasons also have longer, more elaborate couch gags, which can easily be cut in syndication.