Here's just a few of my thoughts
I like to think of the site as a fair partnership; It won't work without content contributions, so its only fair to share revenue, pr, obls etc for that content.
I'm fully of the opinion that the paid site is long and gone; everything is free today. We like free

I'm also finding that clean code and increased content weight with the page is also generating more traffic. So there was a need for a site to have this as standard.
I also needed an aged domain which which to trial the pages, hence the subdomain, later I may port it all off to another domain that is aging at this moment.
Then I thought how I could create traffic and links
Make the links myself (time consuming)
Get others to do it (slow going)
Get other to do it with the adsense incentive (faster going)
Social bookmarking (todays web directories)
RSS feeds as standard
XMLRPC Pings (essential for fresh content)
Then I thought why settle for just organic web search, when I could get organic blog search and news search traffic for free as well

Which at present is pretty equal.
Cheers,
Dave