Hi
remember that they are professional wildlife photographers and to them megapixels "do" make a difference. It means less interpolation to get up to larger sizes , more detail for calendars etc and the fact that they are in competition with other pro and amateur wildlife photographers so they have to get every last bit of quality out of their images.
For normal use for prints etc 8mp is more than enough so don't worry about your 350d
The 40d is a great camera and at just over £500 (with canon cashback) it's at a good price too.
neil