Just like banjo and mandolin can play lead, so can guitar. It's just that so many guitar players are used to being rhythm instrumentalists that they never take to learning any tunes. I was in that rut for awhile until I took up pipes.

So nothing is stopping you. There's a recording by Ryan J. MacNeil (out of Nova Scotia). He is primarily a piper, but one of the tracks is him playing lead guitar. I can e-mail it to you if you want to listen. It's pretty amazing stuff.