I think Stern has done some things that create a cheap impression, but I don't know that I would say that's all necessarily true.
Easy example: people miss the old lockdown bar latch. Honestly the new double latch system, while not quite as convenient, holds the lockdown bar in place way better.
They went to decals instead of screened cabs, but the resolution and quality is way better (assuming your decals aren't peeling).
The support pegs instead of rails are bullshit though.
In my mind the problem is more that they *look* cheap. The art packages post Metallica have all been a little cheesy and just haven't oozed quality and care. The packaging for the game makes it looked cheaper to me. Doesn't mean the parts and gameplay are crap though.