First of all, the 40D and 50D were good at high ISO's. Nikon played catch up until they put out the D90.
How do you know the D300 has better AF performance and ergonomics? Have you held a 7D? Have you seen the AF working? The camera was just announced this week.
You know why the 5D MKII is so hard to find? All the videographers that are shooting video. SLR photographers may not, but there are sure a hell of a lot of video people that were super excited about the 5D MKII and use it. I think it's even getting some time in the spot light for being used in some up coming main stream movie or another.
1) I refer to DPReview's 50D review:
Canon EOS 50D Review: 31. Conclusion: Digital Photography Review
"in terms of per-pixel sharpness the 50D cannot quite keep up with the better 10 or 12 megapixel APS-C DSLRs in the market. At higher sensitivities the smaller photosites are clearly producing more noise (as shown from our RAW comparisons) and so Canon is having to apply more noise reduction to keep to acceptable noise levels, this of course means a loss of detail from ISO 1600 upwards."
And
"At a pixel density of 4.5 MP/cm² (40D: 3.1 MP/cm², 1Ds MkIII: 2.4 MP/cm²) the lens becomes the limiting factor. Even the sharpest primes at optimal apertures cannot (at least away from the center of the frame) satisfy the 15.1 megapixel sensors hunger for resolution."
And finally:
"In some areas such as dynamic range and high ISO performance it's actually worse and that simply makes you wonder if the EOS 50D could have been an (even) better camera if its sensor had a slightly more moderate resolution."
which makes me think, we're probably going to see the same concerns about the 7D now. In fact, after seeing the sample images that DPReview took, I have to be a bit concerned with even ISO 800 performance which shows significant loss of detail and noise. From
Canon EOS 7D Preview Samples Gallery: Digital Photography Review
2) I'm referring more to the 51-point AF sensor on the D300 with that general "AF is better" statement.
3) I never said adding video to the 5DMkII or to cameras in general was a bad business decision. It's obviously making Nikon and Canon some money. However, it doesn't apply to *my* criteria as a customer nor to many other customers like me, and therefore I couldn't give two twats about whether video was or was not included so long as some other feature didn't suffer as a result.