Gregory Maxwell wrote:
Extra parameters in [[Image:]] create scaling problems. If we have a million images, then we'll have at a minimum of around a million thumbs. If people tend to use two sizes, two million thumbs. If they tend ti have two different rotations four million thumbs. It's not so much a disk space issue as it is an ability for the operating system and other software to scale to handling tens of millions of small files.
I don't think this would make things any worse than they are now. In my experience, whenever an image is used on more than one page (counting use in a template as one use), more often than not each page already has it in a different size.