I have been a member of PS, Piano World, and Piano Street for many years, and this issue--exactly this issue--has come up many times.
The issues are actually not all that complicated: the root problem (if it may be called that) is that piano sampling, audio editing, and midi are now so sophisticated that it is impossible to be sure what is a live performance and what is partly or wholly doctored, edited, or transformed electronically.
A friend of mine recently performed a Chopin Nocturne for me at my piano, recorded it with a Nikon D7000, and then substituted a midi-sculpted audio file for the original recorded performance at my wife's MAC.
I have played piano every day now (strictly classical I have to admit) for over 50 years: I could not discern ANY subterfuge in the final product: I was astonished. Shocked. Stunned. Gob-smacked.
So the implications are very plain: unless you know the pianist personally, or you have seen him or her perform, etc., etc.. there is no way on God's good earth to know whether or not something is "real" or "slightly edited" or "super-edited"!!!
Guy's submissions were, for various reasons, transparently midi-edited and employed a sampled piano. This is exactly what I do... I have NO problem with it.
But I completely understand the main issue that it raises: many, perhaps all, piano sites invite submissions as a forum for analyzing and discussing piano technique. That sort of activity is... well... "undermined" where submssions have been altered (whether through midi or audio-editing). Because that is a quite different sort of technique. Piano technique in the traditional sense is only one part of midi and audio editing. It is clear that much of what is done in the edit process is designed, in fact, to overcome technical shortcomings. Hence the notion that it is a "cheat"!!!
Problem is how do you sort out slightly edited from completely fabricated? In other words: enforcement of a rule... any rule... to sort out the different kinds of piano material submitted.
Guy's rendition of the Etudes (both sets!!!) was submitted without the usual sort of clarification about process of creation, and I guess some folks were a little embarrassed that they didn't spot the sampled piano, or the midi-editing right from the get go. Sort of a "Joyce Hatto" moment!
Others just think it's wrong to post stuff that isn't performed live.
Others, which include me, are interested mainly in the beauty of the final result (like a beautiful piece of driftwood), and secondarily concerned with the question of how the result was achieved.
But it's all OK in my books.
Live performances are fine. Edited performances are fine. Midi-creations are fine. (At least for me personally.) But I can completely appreciate the reasoning of those who want prompt and accurate disclosure re which category!!!
Point is: it will have to be an honour system, because there's no forensic science that will provide an easy answer.
Not any more... Technology is too advanced.
JG