I think most people want a wider tire than the stock 225's. And the 225-60r-15 is pretty short at 25.6". Original was 225-70r-15 which is 27.3". So the 225-60r-15 is over an inch and a half shorter than the stock tire.
The nice thing about the 255-60r-15 is that it's 27.1", so it's wider and still practically the same height as the original size.
This is a good chart for checking tire dimensions:
http://www.tirerack.com/tires/tires....l=Radial+T%2FA