Most web apps are not that difficult to program. What needs the most innovation in a startup is the business model. Communicating that locally is hard enough. Remote? No thank you.
Put that all into an imaginary 1-100 rating: you can get a 60-70 programmer in the bay area, or an 80-90 programmer remote. How many points does being local make up for? That's a question specific to your company, but if it's less than that difference in overall developer quality, remote may be a good call.
First, web apps aren't that difficult, it is true. But that doesn't stop web app startup founders from demanding only the best of the best data structure/algorithmic programmers.
Second, web apps are not even close to being the only kind of programming, suitable for remote work or not.