I was an XP user until 4 weeks ago,when I got a new daw with Win 7. I took a small bit of satisfaction in getting XP to continue to work over the years. Big problem came in installing a Native Instrument add on a few months ago. Basically although I got the sounds installed I really had to work with NI (they were good about it) and it illustrated that XP is just not supported by anyone any more and its just going to get worse. Its really not Steinberg thats abandoned XP; its basically everyone that makes software including Microsoft.
Interesting question as to whether C7 needs something in Win 7/8. One thing I noticed is that the Cubase 64x bridge works perfectly in Win 64x whereas I needed Jbridge with XP 64 x.