Ask HN: Why is WebMD so profitable?

I have a question regarding WebMD and it's good financial performance. WebMD is a publishing company similar to (in a sense) the Old School Magazine publishers. However in a time when other content producers are loosing money continuously, WebMD seems to earning quite handsomely?

http://finance.yahoo.com/q/pr?s=WBMD+Profile

Can you help me understanding reasons for it: Here are my guesses

1: Unlike other publishers WebMD reviews it contents from a certified doctor hence people are more likely to trust it over mom and pop blogs.

2: A real good SEO job, since for nearly any health related term it is one of the top few results.

3: Web focused content development, unlike other companies which are still focusing on print media.

4: A niche market and first mover advantage. ( WSJ, Newsweek have many competitors)

5: Aggressive nature of advertisers. Most of the advertisers on WebMD seem to be drug companies which spend significant amounts on advertising, and WebMD represents a perfect platform to reach out to potential consumers?

Also in light of potential competitors like HealthLine (a focused semantic search engine) receiving VC funding. Is content aggregation a good idea as far as healthcare related information of internet is concerned? http://deals.venturebeat.com/2010/04/26/healthline-funding/

These are few reasons I could come up with. Please Comment!