Wow Pink Floyd Dan, you're being kind of a jerk, huh? I never said Coldplay were thieves, or anything similar. They came up with a melody that I feel is very similar to Satriani's. Does that make them bad people or con artists? Of course not.
The legal point that you are trying to make is simply untrue- you could ask my Legal Aspects of the Music Industry teacher here at Berklee, or you could read what Wikipedia has to say about it:
Actual copying
A plaintiff establishes actual copying with direct or indirect evidence. Direct evidence is satisfied either by a defendant's admission to copying or the testimony of witnesses who observed the defendant in the act. More commonly, a plaintiff relies on circumstantial or indirect evidence. A court will infer copying by a showing of a "striking similarity" between the copyrighted work and the alleged copy, along with a showing of both access and use of that access. A plaintiff may establish access by proof of distribution over a large geographical area, or by eyewitness testimony that the defendant owned a copy of the protected work. Access alone is not sufficient to establish infringement. The plaintiff must show a similarity between the two works, and the degree of similarity will affect the probability that illicit copying in fact occurred in the court's eyes. Even then, the plaintiff must show that the copying amounted to improper appropriation. Indeed, the US Supreme Court has held that not all copying constitutes infringement and a showing of misappropriation is necessary.
Long story short, if Coldplay had access to Satriani's music which they probably did since he was on a major label (Epic), that establishes access. ( A plaintiff may establish access by proof of distribution over a large geographical area/B].)
The other part necessary to prove copyright infringement is the similarity. That is the part that is open to interpretation in this case. You obviously think it's not similar enough, others do. That's just how things go.
Oh yeah- if you think Satriani is a speed metal idiot, you'd love Vinnie Moore. Lighten up, dude.