Eighteen speeds versus three speeds is to totally different riding techniques. With the 3 speed you have two choices, spin and go slower, mash and go faster.
Someone who is used to a steady cadence and being able to shift gears is going to have to relearn when they ride a 3 speed. I did. But now I can switch back and forth between them with minimal fuss, just have to remember the reason I am riding the three speed is to enjoy the ride and maybe get there, with a high count multi speed it is to get there fast.
BTW I like that Trek Belleville, unfortunately they WON'T be coming to an LBS near me...I already asked.
Aaron
