Well, I can't tell you one way or the other regarding CS5.5>CS7...I don't know. I do know that the intent was for upgrading be limited to 1 full version back. But things change all the time and I've not heard any specific policy regarding CS7 or if it's even going to be CS7 or if it might be CS6.5.
So, until Adobe makes some sort of announcement, you won't know. However, there is one thing you could do once the next version (whatever the name ends up being) is officially "announced", go out and buy the upgrade to CS6 which you know you are entitled to. As long as you buy the upgrade after the announcement but before CSXX is shipping Adobe's policy has been to provide a free upgrade to the newest version. Of course, that might well change too.