I'm glad you made this distinction. With enough time, yeah, sure, we can be "good" at any of them, but I've seen companies bring people on without a developed skill set in a particular technology only to find out the ramp-up time to be as efficient as someone familiar with it to be much longer than they bargained for.
near the beginning of your startup, you need multi-hat-wearing-swiss-army-knives for developers. once you get traction and growth, you need to bring in vertical expertise.
