Coldplay are just doing different versions of Unforgettable Fire. Now, at least they have good taste in picking that album to rip off, but they have never surpassed the original, and I have no expectation that they will. Maybe they should try something different, but Chris's ego wouldn't allow at, as they might sell less records. Coldplay to me are the modern equivalent of the Police - decent musicianship, a good live draw, the occasional undeniably great single and melodies, but I always get the impression the whole is less than the sum of the parts. All traces of originality filtered out, any semi-provocative or controversial sentiments, if indeed they lurk below the surface (which I doubt) expunged in the interest of commercialism. Now, put that against U2, who released an album criticising Reagan policies right in the middle of the Reagan era, and then proceeded to sell out stadiums all over the country on the basis of that album. (Actually now that I think of it, the Police had much catchier singles than Coldplay, and better lyrics.)
Radiohead started off being influenced by U2 albums such as Joshua Tree and Achtung Baby, but from the Bends onwards they had their own unique sound. From OK Computer onwards they were drifting off into cyberspace somewhere (and I mean that as a compliment).
Radiohead could have been another U2, but it was their choice to go in a different direction.