FWIW, I think you're giving Canon a bit more credit than they deserve. The old 300 2.8 IS, 400 2.8 IS, 500 f4 IS, and 600 were always great lenses and would have worked well with the big MP as they were from a resolution perspective. Really, anything that works with a 7D would work with the big MP because they have about the same pixel density. I see the upgrades to the long glass, at least, as being more about the AF and weight.I think that is why Canon has been doing alot of len upgrades. I think they are making sure that users who will buy a Big MP body will be able to get results out of it via the new L glass. Just MHO, but I think Canon is smart to upgrade glass first.
+1 I have been thinking along the same lines as this, above.