FWIW -- my XD9 (4") has ~15K rounds through it. Everything that's gone in and gone 'bang' has been extracted and ejected without a problem.
Anything can break on any gun, at any time. Mine has run, period. It's run in sub-freezing cold and in 90+ degree heat. It's run in monsoon downpours, and after being ground into Nevada desert sand in a close quarters class. Maybe I got lucky, but that's my experience with the gun. I keep it relatively clean (Titegroup reloads, scrub it out every 6 or 8 weeks), use Slide Glide + synthetic motor oil lube.
If YOU like the ergonomics, go for it. Be aware that there is a difference in balance point between the 3" - 4" - 5". See if you can handle all of those before dropping the $$.
Interesting that you mention that. I've talked to several guys who frequent handgun training classes, and they claim that XDs break and/or malfunction more than any other pistol they commonly see (mainly Glocks and M&Ps).
In fact, I've noticed that on migunowners.org among the pistol trainers there it's a running joke about XD reliability, or lack thereof.