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.
While the 50D looks like a VERY nice camera, I can assure you that you'll be treading into diffraction limited waters once near or past F/8 and purely from a resolution standpoint, if you shot the 40D and 50D at F/11, you'd quite likely end up with about the same overall resolution simply because of the pixel pitch of the higher MP sensor in the same APS-C space. Has nothing to do with the lens at this point.
I shoot on the other side (Nikon) with the D2X and can absolutely tell you that F/11 is the limit (probably more like F/10 if you're really critical) before diffraction robs you of sharpness - and that's with some of the very best glass Nikon makes (200/2 VR, etc), so it's not the glass - it's the pixel pitch of the sensor. This is commonly known - I'm not just talking out of my head or making something up to slam a competing brand. If Nikon comes out with a 15mp DX framed camera I'd be saying the exact same thing - in the cropped sensor, 12mp is about the sweet spot for a landscape shooter IMO.
So that's the big problem - not just with Canon, but with anyone (Nikon, Pentax, whomever) who is trying to move beyond about 12mp on a DX/APS-C cropped sensor - the pixel pitch is getting too bloody small and diffraction rears it's ugly head.
And we won't get into the higher demands on the lenses (you think the less-than-spectacular Canon wide zooms are going to shine on a 50D?) and also focus accuracy and problems with subject/camera movement. High pixel density is nice *when* you get everything right, but it requires far more technical discipline out of the photographer and requires that everything in the "chain", from support system to aperture (that isn't in diffraction city) to focus to technique is optimized or you'll never realize the full megapixel capability fo the camera. And that's with any brand - again, I'm not just picking on Canon here.
Ultimately what I do hope is that Canon takes the sensor *technology* from the 50D and applies it in the 5D replacement. The thought of a FF camera that's affordable (relative to the 1ds-III) and maybe 18-20mp with a very nicely done sensor is somewhat of a holy grail amongst landscape folks, I think. Such a beast won't be so problematic in terms of pixel density/diffraction problems, yet it still will have decent resolution, and hopefully have nice DR. That's preferable (getting the combination correct) versus just playing marketing megapixels...
YMMV of course.