You can even go as far back as 2007 for the MBP and iMac!
Actually for an average user an Intel C2D with an SSD is more than enough for everything.A couple of years ago we've reached a certain level where performance doesn't really matter anymore to 99% of the users, simply because the difference is unnoticeable. I'm also planning to keep my 2011 MBA for a few more years because it's perfect for everything I need. The only thing that could make me consider an update is a Retina MBA, but then I'd rather wait at least one generation until possible glitches are smoothed out. Fortunately Apple is not violently forcing Mac users to upgrade - the fact that you can install Mavericks even on a 2008 MBP/MBA is quite cool.