It's still pretty trivial to mess up memory management and segfault and die. Speaking as a full-time iOS person, I don't think I want to write a backend in Obj-C.
When I flub a strong/weak reference on a phone, my app crashes. The user is mildly inconvenienced as they launch the app again.
When I flub a strong/weak reference on a server, my app crashes. That server is now down and my ops guy (probably me) will have some unkind words for me, particularly if it's in the middle of the night.
It's tempting to say at this point "well, don't flub references, n00b", which is much easier said than done. Bear in mind that we did use to write webapps in C - we moved to higher-level, more resilient languages for a reason.
I don't mind Obj-C/Cocoa. I'm a graphics guy at heart, so the closer-to-the-metal implementation makes me happy and lets me spin all kinds of neato magic with custom UIs... none of this is necessary serving data off a server.