So what's the problem? You don't shoot portraits with a wide angle lens, do you?
No, neither do I have the room to stand back enough to use a 85/100mm portrait lens when the camera is cropping it for me. I don't want the DOF of a 40mm lens (long end of 17-40) eventhough it's pretending to be a 70mm! When I'm shooting with a 50mm lens at f4 I get the same DOF of a 50mm lens at f4 eventhough it's pretending to be a 80mm. If I want the DOF and look of an 85mm lens at f4 I don't want to be forced to step backwards!!!
No major disadvantage? How can you qualify that statement over the entire spectrum of photography? If FF really wasn't an advantage then the 1Ds mkII wouldn't be selling, instead of still being waiting list and the D2X would have taken over the market which it has completely failed to do, whatever the praise.
There is no wide angle 24-70L equivalent in the canon lineup, the 17-40 isn't as long or wide and is a stop slower, the 16-35 is even worse for the long end. The 24-70 range is there for a reason, it is an incredibly versatile 'normal' zoom. No wide angle equivelent is as versatile, as sharp and as flare free to carry out the same job.
That's not including the crop viewfinder, however bright, the far too big AF points that don't allow precise AF (Canon admit to using the same size AF sensors in the 1D as the 1Ds, hence the sensor is covering a larger area).
Is Edge Sharpness really an excuse? I would put my 24-70L on FF against the 16-35 on a 1.6X crop, same FOV, any day. I can garuantee you which will win sharpness wise, if you take it outdoors on a sunny day then you might as well not bother.
I'll repeat, the nearest equivelent to the 24-70L in 1.6X crop is a 17-40L. Eventhough the long end 'looks' like a 70mm, I couldn't use that for portraiture or pictures that need shallow DOF , period. That to me is an incredible disadvantage.
A crop sensor may be better for landscapes though I don't buy it coming from Med Format, but for me and apparently hosts of photographers still shooting film or using FF cameras, the crop is more bother than it's worth.