L series lenses are 'professional' lenses. 1-series bodies are 'professional' bodies. So, an EF-S 'professional' lens, which wouldn't work on a 'professional' body, is a non-starter.
I suppose Canon could slap a blue ring, magenta ring, whatever, on a new series of lenses that are 'semi-pro' EF-S lenses with better build and sealing. But consider - among APS-C cameras, currently only the 7D has a reasonable level of weather sealing and high-end build quality. Comparing that to the the sheer number of other APS-C models with lesser build/sealing, it may not make a lot of (financial) sense for Canon to develop sealed lenses for a small image circle camera since the market just wouldn't be there.
JR said:
I remember when I has the 17-55 2.8 IS on my 7D and I love having the IS for video shooting. Since moving to the 5D mkII, I am a bit frustrated that they dont have an equivalent 2.8 zoom with IS (the 24-70 2.8 I mean) and that the only option for IS would be the get the 24-105 f4 which is a no go for me for indoor shooting.
It's a common fallacy. In fact, the 24-105mm f/4L IS on FF outspecs the 17-55mm f/2.8 IS on APS-C in nearly every way. Consider - in terms of focal length and DoF for the same framing, the FF equivalent of the 17-55mm f/2.8 is 27-88mm f/4.5. So, the 24-105mm f/4 is wider and longer, has 1/3-stop shallower DoF, and still has IS. Going from an APS-C sensor to a FF sensor gains you 1.3 stops of improved ISO noise performance based on total light gathered, meaning you can bump up the ISO on the 5DII by one stop to compensate for the loss of light going from f/2.8 to f/4, and
still get nearly 1/3-stop less noise. The only thing you really lose is the functionality of the high-precision f/2.8-sensitive center AF point - in every other way, the 24-105mm on FF will be better than the 17-55mm on APS-C.