I'm not sure that I would describe the D800/E as harder to get sharp shots with (although that may be the end result). I think it is that the D800/E exposes shortcomings (whether it be in equipment, technique, or subject) sooner than with a lower resolving camera.
Ming Thein brings up very good points. Also, imagine a line that is a several pixels wide (on the D800) that has slight variances in black/grey shades across it's width. The resolving power and the ability to distinguish subtle changes in shades across the line will be exposed on the D800 and the line may not appear as a sharp black or grey line...because it isn't. On a lower resolution camera, there will be fewer pixels used to render the line and they may all be represented as a single dark grey or black shade. This will come across as a nice hard edge.
I find that when I expand a tack sharp image from the D800/E to 100%, the image is so impressive that I try to expand the view farther to see more detail. Obviously that is not possible, but what I want to convey is that the pixel level sharpness or acuity (not sure if that is an appropriate term to define a pixel) fools me into thinking that there is more to see. Images loose this characteristic as the ISO increases due to noise (or blur), however.
On the other hand, I think what Ming Thein is saying is that there really is not an advantage of the D800 for photographers who are not maxing out (or cannot optimize) technique in the type of situations that they shoot. If the D800 is your only camera or your other camera is a point-and-shoot, I think the D800 is an excellent tool for nearly any type of photography...just don't expect razor sharp pixel-level viewing on all photos because in almost all environments outside of a studio, there will be "pixel-robbing" conditions conspiring against you.