Absolute rubbish. Understandable I think - and people have been saying this since MIDI was invented, but MIDI is just a communication language and like any real language, has the ability to be used beautifully or rather awkwardly. MIDI gets blamed all the time for mechanical, unrealistic performances. The blame for this is 100% the producer's. I can only speak for my experience but I produce lots of piano music - played by a real concert pianist, and some is recorded on his Yamaha grand piano and some is produced inside the computer, driven via MIDI from a keyboard. I cannot tell which is which now we have lots of recordings without opening the cubase files, as we didn't actually write it down! MIDI gets a bad rep as somehow being awful, and it absolutely is NOT!
A track sounding like a live recording or a record is a totally different thing - but again, it's down to the skill of the recordist or editor. The quality of sampled and synthesised sound produced inside the computer is now so good (assuming you spend a few quid) that it's impossible to tell. In fact, the quality of some packages now is so good that I could not record it as well in my humble studio with it's small space, less good acoustics and probably not as good player!