A number of websites are reporting that Sony has recently updated the database of their backwards compatibility status-checking application. Some speculate that the recent scarcity of the 60GB models have sparked increased sales of the 80GB model, thus prompting the update to the website. Since the two models differ in their backwards-compatibility implementation (the 60GB is hardware-based while the 80GB is software-based), the support for older games varies. One author is already reporting that the 60GB model is significantly better.
This comes to no surprise to the European crowd since the European consoles are sold without the backwards-compatibility chip, and the European compatibility site has already been up for quite some time. The move is aimed at reducing manufacturing costs, which may have something to do with analysts' prediction that the 80GB model will drop to $499 USD in time for the holidays. The move may also be needed to compete with the Xbox 360, now that the 60GB PlayStation 3 has been discontinued.
Firmware updates are expected to incrementally improve the support for PS and PS2 games, but if you're seriously concerned about backwards compatibility, you'd better check Sony's website before purchasing the new model: http://www.us.playstation.com/Support/CompatibleStatus