One of my best sounding electrics, acoustically, was one of the most difficult to get to sound good amplified. I've seen other posts here saying similar things. Your ears just can't hear all the subtle nuances & frequencies of an unplugged electric guitar. PU's will trasmit part of the acoustic tone, not all of it, and there's many other components in the sound signal that color the tone, like pots, cord, amp, tubes, speaker, etc. Even room acoustics change the sound.
Odds are a professionally set up guitar will almost always be chosen over one with rusty strings, intonation off, a slight back bow in the neck, overly high action, wrong string gauge for you, and the PU's too low. 10 minutes and that guitar that feels & sounds substandard, could 'sing.' I think most guys that demo a guitar get a warm fuzzy feeling based on easily changed variables, and while they get a good guitar, they rule out many others that need a few minutes TLC to sound great. To me, demos mislead as often as they guide. If all the guitars in a store had great set ups, and PU's that matched the wood well, then you could tell a lot by demos, but most guitars in music stores don't fall in that category, regardless of price.