There are a number of details on what models support what features. As for official Mountain Lion support, I was going from memory, but I was close. The late 2008 or early 2009 thing on the macbook refers to some ambiguity within the lineup at that time. The white macbook sold into 2009 was definitely dropped, but it falls into what I mentioned about terrible gpus. It definitely doesn't support everything from 2008. Anyway this is detracting from my point earlier. If OSX is moving toward an annual release cycle, they're likely to become more aggressive on chopping old models. The other point being that larger developers tend to follow Apple. They don't like to support things that are no longer supported by Apple due to more work for a smaller customer base. It may be problematic to support the older ones on many different OS revisions.
http://support.apple.com/kb/HT5444