I have seen similar statements and rifts with EQ1 players. The most die-hards come from the people at the highest levels of the game. They don't want to abandon the power and prestige they enjoy as a level 70 whatever to start over in a new world full of the unknown. They also feel they've put too much time and energy to get where they are in EQ1 to just close up shop and leave. I was no different at first, having played EQ1 for 5 1/2 years and knowing things like the back of my hand. However, after I got accepted into beta and when I actually went through the newbie experience and everything, I found myself enjoying EQ2 much more than EQ1 and was much more willing to abandon it to try EQ2. Hell, I'm sitting here chatting on message boards and playing Civ instead of dinking around with EQ1.
At any rate, expect many end-game players to be set in their ways for awhile and talk about how EQ1 is better or that EQ2 sucks or whatever. Most feel they've come too far or still enjoy EQ1 too much to care about EQ2 or any other games. The problem die-hards in EQ1 are eventually going to face is that EQ1 is going to attract less and less new players as time progresses. This means as older players quit, they'll be less people coming in to replace them. It'll be a slow process, perhaps years in the making, but many will leave EQ1 in time for one reason or another and choose another outlet, be it EQ2 or something else.
As far as how EQ1 players treat people leaving for another game, it never ceases to amaze me how worked up some people can get. When I decided to retire in EQ1 recently, I had one person (for the record, NOT in my guild) send me a tell saying how my leaving was totally inconvienant to them and that a true friend wouldn't just up and leave. To that, I gave them the finger and said that EQ1 is a game that I play for fun, not a chore I do to for other people's benefit. Most were nice otherwise, just surprising how seriously some people treat this crap.