Parallels Desktop 6 and Parallels Desktop 7 are the same "product", but you require an upgrade to move from one version to the next. Without the upgrade you will alway be looking for the latest build of your current version of the product (in your case Parallels 6).
Parallels 7 was released on September 6th, 2011. You can see the "free" upgrade offer here: http://www.parallels.com/keyfor7/. The highlights seem to be that if you purchased from an authorized reseller between August 1, 2011 – October 31, 2011 you qualified for a free upgrade, but it had to be claimed by November 15th. Otherwise there is a $49.99 upgrade still available for owners of Parallels 5 & 6.
Looking at the Parallels 6 support: http://www.parallels.com/support/pdfm6/ it says that as long as you've upgraded to the latest builds you should be able to run Lion, but that it does not take special advantage of new Lion features (whereas Parallels 7 does). Parallels has only just stopped supporting Parallels 4 (when 7 was released), so it would appear that you should be able to stay on Parallels 6 (as a supported version) for at least another two versions if the features in the latest versions don't offer enough value for you to upgrade.
Note that I don't work for Parallels, so this is just information I have gathered from the site. Depending on your circumstances you may want to contact Parallels Support and explain why you missed the upgrade period. Maybe something can be worked out.
Last edited: Dec 31, 2011
