Actually, no, I take that back. The thing that bugs me most recently is the tendency for studios to keep "reimagining" cool stories (such as Robin Hood, Arthur, and so on), with either "gritty", "realistic", or "the truth behind the legend" versions, when the legend/myth is usually far better.
Yeah that mystifies me too. My particular pet peeve is how ninja's have become this wholly artificial construct so that they barely resemble their historical origins and yet their historical origins are so damn cool that there was never any need to create a variant.