From Jan 1, 2013, only CS5 owners can upgrade to CS6.
Everyone else must pay full price for CS6 or join the Creative Cloud.
Last year, there was a special offer from Adobe for CS3 and CS4 owners to upgrade to CS6 but that offer expired on Dec 31, 2012.
http://www.adobe.com/products/creativesuite/faq/upgrade-policy.html
The upgrade net's been tightening for several years.
Until CS5, there was a "3 versions back" upgrade policy so CS2, CS3 & CS4 owners could upgrade to CS5.
With CS6, that was abruptly revised to a "1 version back" upgrade policy.
Only CS5 owners qualified but there was an outcry from everyone else - traditional version skippers - who suddenly, without warning, had no chance to upgrade.
Following a high profile public campaign http://scottkelby.com/2011/an-open-letter-to-adobe-systems/, Adobe offered a 12 month window throughout 2012 for CS3 and CS4 owners to upgrade which expired on 31 Dec 2012.