Don't get me wrong, Ti is wonderful stuff. I've got a Ti road bike sitting right behind me as I type this that has given me tons of good miles since 2002 and will continue to do so as long as I can foresee. I've run Ti bolts, Ti saddle rails, all manner of Ti parts. It's wonderful stuff.
All I'm saying is if you're a big person, Ti spindles are not a good idea. It's just too small of a diameter to capitalize on the strengths of Ti. Hell, even Grace has had a Ti spindle fail on her eggbeaters, but that was several years back and the design was pretty rife with stress risers. She's been on full Ti Egg 11s for a while now, and they've been fine.
Also, I've had several pedals with non-stainless spindles. Sure, it can rust, if you're not paying any attention to your components. Otherwise, grease keeps that from happening.