I think that it is a mis-print. It says under devices that support both new functions:
MacBook Pro (17-inch, Early 2009)
MacBook Pro (17-inch, Late 2008)
If I remember correctly the 17-inch MacBook Pro wasn't updated in Late 2008, only the 15 inch went unibody (with the 17-inch following in early '09) so I can only assume that it is meant to say MacBook Pro (15-inch, Late 2008). I have one and it is supported too, not that I would want to lose the 3-finger navigation anyway but feels nice that my computer hasn't already become a device that is losing compatibility with new features, that's never a nice day!
Yes that sounds plausible - agree with you re the ageing devices. I have a MacBook(2006), MacBook Pro 2007 and my iMac 24"(2008) which are just about starting to get left behind - I don't have the income to replace these nowadays so I hope Apple keeps my late 2008 model supported for as long as possible with these new features.
Ah well.