Nah, I've seen a handful of unbreakable weapons as I've wandered about. And you're right, they are indeed very handy for smashing open containers. Isn't there a chance of reduced treasure when you use an item to smash open a container, though? I don't recall if anyone ever actually outright stated that, though, so I could just be drawing an assumption based on my experience with other games that have involved breakable containers and smashable locks.
In regards to doors, though, I don't think it's a huge deal. Most doors have keys hidden within walking distance, anyway. That, coupled with the fact that many doors are apparently purchased at the "Ironwood Super Door Outlet" make unbreakable weapons kind of welcome. I mean, seriously, even folks in the starter town apparently sank tons of money into purchasing the sturdiest doors available, to the point where I went through one-and-a-half handaxes just to chop down an interior door in the local tavern.
