For landscape photography the increased MP will be useless. Stop down to f/11 and compare a 50D file to a 40D file; in terms of resolution there will be no difference.
Your statement is exceedling far from the truth. For landscapes, MP matters. Lots.
Or perhaps you just print 4" x 6" prints?
What does F11 have to do with resolution and/or MP?
Nothing, unless a caca lense provides too early diffraction, yea? Usually that happens at F16 or down from there, lens depending.
For landscapes, one cannot get enough MP. Of course DR is more important, but lets not throw the MP out with the bathwater.
By the way at 16" x 20" prints, you will see a difference between 40D & 50D.