Good mechanical disc brakes exist. I have Avid BB-7's on my mountain bike, and there's a lot to be said for the fact that every mom and pop bike shop has cable and housing on hand.

Are they as nice as hydraulics? No, but they're pretty damn good and easy for anybody to maintain. At the level I ride, that's a worthwhile trade off.

I've done brake jobs on my cars and I've done every job there is to do on a bike short of replacing a headset or rebuilding a fork; I don't have a burning need to bleed more brakes.

There are some really crappy low-end mechanical disc brakes around, but the TRP Spyke and Avid BB7 are solid and commonly found on touring bikes. If you plan to cycle 30,000 km through lots of remote terrain (e.g. Alaska–Ushuaia or Europe to Cape Town via West Africa), then they are as trivial to maintain as rim brakes, without however destroying your rim.

I have cycled down some of the world's great mountain ranges, and I have never had complaints about my Spyke's stopping power.