I wrote a somewhat in depth response which has now been included into the original posting. I've cut and pasted it here for your reading pleasure, but for the full effect please read the linked article above.
Assuming of the 5 million or so MMORPG players that are playing out there (which I'm doubtful of, but we'll play ball) it is a drop in the bucket compared to the number of players that would play MMORPGs if they didn't come off the line like solid brick walls. There seems to be little, if any, move to make MMORPGs more accessible (please don't read that as simpler) to the mass audience.
You hit the idea on the head that RPG gamers come from a different breed. I'm not so sure if you can limit it to past systems. You need to remember that back in the day of the Atari 2600 there was almost TWO TIMES the number of gamers in the market. Yes you heard that right and if I could get the link to Nolan Bushnell's speech I would :P
RPG gamers also come from the roots of D&D (duh!) and that is something you can compare to the experience of being a non-Atari gamer back in the day. It has never and will never be about the graphics, technology, or the feature list.
It will remain to be about the PEOPLE.
Also I think you are complete backwards on people coming in through WoW and moving onto "harder" games. It is quite the opposite. People get stressed out on the overly time sink methodology of games like Everquest and jump ship to the more casual friendly WoW.
WoW in no ways should be seen as a market entry point for new gamers. It is bringing in new players, but the experience it promotes DOES NOT make people get into what you are classifying as harder MMOs. Don't confuse more time consuming with harder. It could be debated for years how hard WoW's end game content is compared to EQ's. Its the delivery mechanism that counts here and WoW delivers a system that a new gamer isn't going to be destroyed in.
On another note I don't believe time played is something the MMORPG market has cornered. I would even wager that the average Counterstrike player has more time online than most MMORPG players over a much shorter time span. Sure there is a lot of cross population amongst FPS players and what games they are playing, but the same is true of the MMO market (except within the HARDCORE circles).
What I'm getting at is that ONLINE play is what is stealing the market. MMORPGs are just charging for that time and hence are getting the attention of the venture capitalists looking to fund projects that are going to prove to be a genuine revenue stream.
Video gaming was born in the social aspect. It was not something that was developed as a solo experience. Pong (or Tennis for Two) was two players remember. The majority of early games focused on playing together. It wasn't until after the video game crash and the eventual launch of the original NES that spurred more single player games.
You give players a way to play together and they're going to eat it up. This is something MMORPGs have been charging for, but they by far do not have it cornered.