Quote Originally Posted by Lord Vukodlak View Post
Well Piracy's not quite as good of an example, by keeping their ship they can steel five more and sell them. A magic weapon isn't required or that necessary to rob caravans, but a ship is required to steal a dozen others.
Maybe not required, but it's definitely helpful. If you plan on doing something dangerous on a regular basis you want to minimize the risk however you can. Having a magic sword or armor might mean the difference between stealing a huge amount of loot and being killed by caravan guards.

Also, some magic items can be looked at in a military context. A high ranking knight with a +5 sword is carrying the fantasy equivalent of a fighter jet. It's expensive but not overpriced for what you need it for (protection of the realm, defeating evil dragon, etc.)