does the eye see better thru the eyepiece than the sensor can reproduce?
With an SLR, I doubt it. Remember that the image you see in the VF is not the direct image from the lens: it is an image scattered off a ground glass plate after the image from the lens is focused on that plate. This reduces the resolution significantly below what the lens is capable of: I have read comparisons that high end profession video camera EVF's of about 2MP match or exceed optical VF's for detail. If so, DSLR sensors easily outresolve SLR VF's.
Range-finder VF's are another case; there you see the direct image from the VF optics.
P. S. I think Jonathan has it right on the smaller apparent image size in the VF: small versions of images can look extremely sharp. How many time have you got a shot that looks sharp in a 4"x6" minilab print, but gets a bit mushy when you reprint at 8x10, or even 5x7?