well, i guess softsynths appeal a lot to non-keyboard heads, like myself who happen to like synth sounds, but can't really play, and/or don't have the cash to sink on a minimoog.
for $70 you can get
a native instruments pro 52 that does everything that a prophet does, and you don't have to worry about maintenance, repair or any of that stuff, not even really playing the instrument. you can just program your sequencer and hit play. i know this sounds kind of disregarding towards keyboards, but don't get me wrong, i like synths and keyboards, i just don't know how to play them, and i don't have the money to buy one or pay for tuition. not now at least. it's hard enough for me to dedicate to learning one instrument.
i think hardware is a lot cooler to have, but software is much more cost-effective, and the possibilities are virtually limitless.
my music is not synth or keyboard-driven at all, so i wouldn't want to spend a truckload of cash on synths, that i'll be using for a while when recording, and then forget at home when i hit the road (my band has no keyboard player). so software is the way to go for me. however, i keep hearing of professional musicians who carry a laptop around with a bunch of softsynths installed, that they can play in real time onstage.
the ones i recommend are
the native instruments pro 52 (replaced by
the pro 53), native instruments b4, jxsynth and steinberg's model E. i have a few others' demos, and i'm still learning how to use this stuff, but i think i'm going to be 'converted' real soon.