Most of your examples have raised large amounts of VC funding. It's debatable whether they "need" the funding to success, but they certainly wanted it enough to eat the dilution.
They have raised, but they didn't raise until they were profitable -- that is, WELL past "default alive". They are remarkably different in this respect than essentially every YC startup.
Pretty sure Fog Creek has never raised either, while having 50-100 employees.
The overall point is that you don't have to be a one-person business to grow at a slower but "healthy" rate.
With the above examples: imgur has raised $40 million and can barely keep one website running. GitHub has raised $350 million and can't seem to add new features or fix existing features. 37signals did fake funding just to get connections, but they at least isolated themselves and stopped trying to infect the rest of their world in their hype bubble.
