I know I'm basing my numbers (which are largely pulled out of my ass, no argument there) on exceptional indies rather than the average. That is intentional, and not a mistake at all. As I implied, more than a few indie games are shit, or at best, mediocre. Many of the games listed in that blog you linked to are a good example of this. I don't expect or want Sudoku clones or casual puzzlers to sell 50,000+ copies, although occasionally they do; on the other side of that same coin, sometimes a truly excellent indie tanks for whatever reason.
My point being that if the average indie game is mediocre and forgettable, as has been my experience, then from a certain point of view it's equally meaningless to base your numbers on that average. I'm not "attacking" indie games here, but the fact of the matter is that there is always chaff to separated from the wheat. Popularity doesn't always equate to quality, but anyone can create an indie game, and a lot of them are mediocre. Most people's work in life is mediocre. That's what the term means.
You mentioned Jeff Vogel, and I should note that I've been playing Spiderweb Software games for many years. I love most of the Spiderweb Software games, but they're extremely niche titles and their appeal has always been very limited. Do you mean 5k for each game, or 5k total? I've read some of his blog entries before, but it's been a long time since I have. 5k per game at $20 a pop seems quite appropriate. He's essentially a one-man development team, and if he spends two years developing one of his games which then sells 5k copies at $20 apiece, he's earned $50,000 per year for his work. That's more than a living wage. It's not as though he's spending tens of thousands of dollars on art or sound assets.
I'm as unhappy as the next guy when a deserving indie tanks or simply isn't very popular—don't get me wrong. I do however believe that basing your numbers on an ocean of mediocre titles is equally misguided. Somewhere in-between is much more appropriate.