Satriani sure thinks so, because he's taking Coldplay to court over it. And, yeah, they do sound pretty similar. It's kind of eerie, actually.
In the end, though, I'm kind of skeptical that it matters. The melody is pretty simple, as is the chord progression, and it's hard to copyright something like that. The Beatles didn't sue Beck because "Loser" stole the outro melody from "Hey Jude." Civilization is theft. It's either an excellent and unlikely homage or just a cool coincidence that Girl Talk should exploit someday. The only purpose of this suit is to increase the profile of both artists in the media, although even that is somewhat questionable because there's basically no crossover between Satriani's and Coldplay's fan bases. Few Coldplay fans are going to hear the Satriani track and say, "Hey, that sounds pretty good," and go snag If I Could Fly off iTunes. Likewise, no Satriani fans are going to hear Viva la Vida (if, indeed, they've somehow missed it to date) and say, "Hey, these Coldplay lads have some talent." Mostly, they're just going to think Coldplay are a bunch of tools while Satriani is even further deified on the pantheon of Guitar Gods. Maybe that's the point.