What exactly is IS and why don't we see 3rd party competition?

I don't think IS implies L glass. Definitely not. The 28-135 and 70-300IS are examples.

Do you think lens technolgy has changed that much -

the 70-200 f/4 is a terrific lens with superb AF, build, and optical performance. It is razor sharp at F4 . I doubt it would be easier to make it 'better'

So the 70-200 f/2.8L IS vs. 70-200 f/2.8L would be like this:

IS version would win, with every same settings as the non-IS, on a tripod, same apertures, with mirror lockup and remote?

Sigma's called OS and Noink's is called VR. Minolta/Sony wants the best of both worlds and calls it OIS.

So no-one else does IS.

actually some say that the non-IS is sharper. so in those circumstances, for one thing IS wouldnt be doing its thing, and serves no purpose. but the difference in sharpness would be minimal, perhaps unnoticable.

I would be interested to see a comparison between (for example) the 70-200mm F2.8L and the 70-200mm F2.8L IS *at a shutter speed where IS is not a factor*. Ideally using shots with IS enabled and IS disabled.

It's reasonable to assume that the IS lens will give a lesser image quality than the non-IS lens, due to the extra glass in the way, but I would like to know if, at shutter speeds where you do not need IS, it's preferable to switch IS off, or leave it on.

An extra element group that isn't even cemented in place? You'd think it'd be a recipe for disaster but even side-by-side on a tripod you'd be hard pressed to see the difference and in practice it's a proven winner. I'd bet the competitors would love to have Canon's seemingly endless ability to plug IS into virtually every focal length.