You have never seen so many suggestions that way? You must not read the Wizard "Casting Calls", then.
And realistically, you can look like the character (or what the general consensus says he or she looks like) and be a good actor & still not do it justice. (Brandon Routh)
So I would rather have a REALLY good actor & maybe they can work with the rest. Truth be told, I think Peter Parker (for example) looks more like Charlie Sheen than Tobey Maguire. But I wouldn't want Charlie in the role. Hugh Jackman is pretty; Wolverine is ugly. There are countless examples of actors not looking quite like you'd want the character to look but doing an excellent job.
Did anyone think Downey or Ledger looked the part a year ago? I sure didn't.