The numbers above are for American bloggers, according to the Bureau of Labor Statistics, where I don't find the blogging numbers in the linked table, but they may be elsewhere.
Embedded table found at The Moderate Voice, citing an article at the WSJ:
The best studies we can find say we are a nation of over 20 million bloggers, with 1.7 million profiting from the work, and 452,000 of those using blogging as their primary source of income.My "income" from blogging so far consists of two T-shirts from Neatorama. Since I do review books, I've thought about joining the Amazon referral program, but reading other people's experiences decided it wouldn't be worth it. And I intend for TYWKIWDBI never to have those annoying hyperlinked advertisements.