This is absolutely wrong. At best, the 50D noise profile was no worse than the 40D's. The only point of contention was the reviews that said the 50D was noisier than the 40D.
No, the 50D's noise profile was better in the frame than the 40D's. It was slightly worse if you insisted on blowing shots from each up to 100% and comparing them at the pixel level. But the 50D's higher resolution more than made up for that.
The 50D's biggest problem was horizontal banding at higher ISOs (primarily after you started to exceed 3200), but that's something that can, for the most part, be dealt with in software.