Well it’s just that DPreview concluded that the Increase in MP of the Canon EOS 50D over the 40D brought with it too much noise.
Here’s the part that is worrisome to some
- High ISO performance worse than 40D
- Reduced dynamic range in the shadow areas compared to EOS 40D
- Per-pixel detail not as good as on good 10 or 12 megapixel camera
The 50D however has 4.5 MP/cm² pixels density while the New Canon EOS 5D MarkII has a pixel density of 2.4 MP/cm².