I would not a happy camper with no XP support.
Mircosoft is supporting XP til 2014 why would CCleaner stop before then, that would not be smart.
Also, I guarantee the 2014 support date will be extended, they always are.
Win7's success is greatly exaggerated, downgrading happens a lot, but it's still reported as a new Win7 sale. Just around 6 months ago I bought 2 new Dells with Win7, but downgrade rights with XP Pro pre-installed.