I find when the frets are close together, it's hard to apply pressure and hold a note, because the length of string between the two frets is very short and therefore more rigid - I always seem to "lose" high notes and get a buzz from the next fret down.
I've never had a scalloped guitar, but I had a Yamaha Billy Sheehan bass with scalloping on the top few frets, and it made it noticeably easier to get those notes to sustain. I'm not sure why exactly - I guess you can sort of hook your finger round the string and pull it on to the frets as much as just pushing it.
That bass also had smaller fretwire on the top few frets, like Jake E Lee's guitars - which also seems to make it easier to grip the strings.