Actually, that's probably the most naive of the romantic notions of doing a startup. First of all, the things I described apply to businesses, not only VC-backed startups. Just because your company is small doesn't mean you're suddenly immune from talking to customers and dealing with bureaucracy. If anything, you spend more time talking to your customers when the base is small, because everything is so much more precarious.

Second, the number of "lifestyle businesses" that exist as single-founder-tech-guy-and-a-computer are so vanishingly small as to be unicorns. The people who claim to do that are either secretly making most of their money doing consultancy (which is fine, but it ain't a 4-hour work week), or they're in such a bizarre niche that they've built a knowledge and/or distribution moat around their business that is virtually impenetrable, through years of backbreaking work. Your example of "app store" developers is particularly on-point: it's notoriously rare and difficult to find a product that has a sustainable business model in that marketplace.

Law of the universe: if you want something, there are millions of other people out there who want it just as much as you do. Any business opportunity that is simple enough to be achievable by a relatively unskilled single-founder-with-a-computer, yet lucrative enough to support that founder indefinitely with a four-hour work-week, will invariably attract competition from the undifferentiated masses who don't want to work, either. So you're either competing with those people (hard) for a small pie, or you're trying to build a growth business in a large market (hard), or you're failing (hard), or you're getting a good job (hard). There's no free lunch.