Reading this from Nokia, it sounds like it will be for all WP users
Source
"Rovio ? The company is building a dedicated development team to create titles for Nokia Lumia and the wider Windows Phone ecosystem, with the goal of publishing all future Rovio titles ? including Angry Birds Space ? on the platform as quickly as possible."
Keep in mind they mention exclusives on this page, but never in this section
So I have been waiting for this for quite a while, not because I'm obsessed with Angry Birds, but I feel Windows Phone shouldn't be blown off by Rovio. It's been quite a while since they said "it will be released as soon as possible". Now with WP8 coming up it's leading me to think they will announce it when WP8 is released. Any word on whether this will be coming to WP7 or will it only be available for WP8?