General IT services vs mobile development company: which one inspires more confidence?

Personally, when I browse the websites of companies that provide mobile app development services I find myself turn off if they also do other things.
I feel like there is no way a company can deliver a quality iPhone app if they also deliver websites, backed, other platforms, webapps etc.

How do you feel about it?
If you see other "fields" among the one you're interested in, does it convey expertise or just someone trying to work on anything they can get?

Obviously keep in mind we're talking about iOS apps.