I was actually intending to test that assertion with a new article in the near future, but CDR-Info beat me to the punch. I don't mind, though, because they did a fantastic job; check out the article here. After telling you everything you wanted to know about the various recordable DVD formats, they move on to the testing, which is exhaustive. They tested eight types of media (two examples of each media type) using five different recorders, then tested compatibility in twenty-seven standalone DVD players and twenty DVD-ROM drives. Say it with me now: Daaaaaaaamn. If you're interested in how well one of the tested drives did in terms of compatibility, follow this link and click on the player you want to see.
On a more general note, things have certainly changed for rewriteable DVD compatibility since I did my test. At that point, I recorded only a 36% compatiblity rate for standalone DVD players. Since then, things have improved considerably: CDR-Info reports a compatibility figure in the 86% range for both DVD-RW and DVD+RW. DVD-R, however, still rules the roost, with nearly a 97% compatibility rate. Interestingly, DVD+R barely does better than DVD+RW; makes you wonder how it would've done if it had been out during my testing.
Of course, with an increasing number of companies making DVD+RW drives, and even Pioneer making its next-gen drive a dual-format writer, it's looking more and more like the best man won't necessarily win this unusually bloodless format war. But seeing how much compatibility has improved in the last year and a half or so, in a few months it probably won't matter one way or the other.