Actually, that's typically what does occur as part of gentrification. Typically a bohemian neighborhood has all sorts of interesting indie stores selling books, art, antiques, etc. But these stores aren't that profitable -- a chain retailer can pay much more rent and so the owners evict the indie stores.

True, but generally the bohemians and artists are the first ones to replace the working-class character of the neighborhood with their own, until they themselves are replaced by young urban professionals...

Comparing the wide Internet to a neighborhood with fixed space constraints is a rocky analogy to begin with. The foundation of a new city would be more appropriate, starting with a small population of intrepid explorers in a wild uncharted wilderness and growing to a massive commercial behemoth...

Facebook and the like aren't the Walmart of the web though, they're the Wholefoods and sushi bars; Craigslist would be the closer Walmart equivalent; shoving out weaker sites while still being pretty lower-income