There are probably more people playing Windows Reversi (or any of the other windows net games) than Half-Life.
Maybe, if you exclude CS, DoD, TFC and every other HL mod from the equation.
I wish that the PC had the name protection that XBox Live has, as someone has already taken my Battlefield Vietnam name "John Rambo"...
Yeah...good luck ever beating everyone else to that one.
I'd say MMORPG makes up less than 1 percent of online play, because I think over 99 percent of people aren't dumb enough to keep paying to play a game that have already bought.
In spite of your "evidence" to the contrary, it's probably a substantially larger portion of the PC online community playing MMORPG's. It's safe to say they also spend a lot more time at their "hobby" than your average FPS gamer.
Also, keep in mind--and this is one big issue the "PC vs. Console" article failed to factor in--PC MMORPG players often pay more than just the initial retail cost and monthly subscription fee. For example, how many purchase-only expansions are there for EQ (seriously, I lost track)? Pile the prices of the original and all its expansions together with the monthly payments, and you've got some people who've been milked by one game
for maybe $500 or more.
You could go a step further and consider peripheral factors like lost wages (calling in sick to camp the Froglok King) or the +20 Whatever you picked up on eBay, but these only provide negligable, indirect benefits to developers (through increasing obsession with their products) and, in light of at least one suicide, could be seen as negatives.