People who like the PvP, stuff getting, and action of WoW and such leave because PS does not deliver on that aspect, not because of the focus on roleplaying. If the game was fun for them, they would stay despite having to leave their l33t behind. You will find that people are very adaptable and compromising when it comes to something they really enjoy.
Truth be out, and this'll probably get me banned.

but I am also the guild leader of a fairly large guild in WoW. All that you mention kills WoW as well, and people leave all the time because of that damn l33t attitude. I have members level to 70 and then stop playing as soon as they hit that wall and realize that there is only PVP awaiting them, and that kills our PVE aspirations because we can't seem to get them all coordinated at the same time. It's one of the main reason I'm here, because I can't stand the direction WoW is heading, which is nothing but PVP. The affect WoW has had on the market that is probably affecting you is that they set a standard for MMORPG's that you are being measured against. They dumbed the genre down a ton, and the direction the market is going is to simpler PVP based systems and less on hard core PVE. Look what happened to Vanguard. There are also a ton of people out there who can't stand EQ because of what Sony did to it, and quite frankly, PS is more of a clone of EQ than anything. People will come here, realize that PS has the same frustrating quest dialog engine that EQ had, and will just leave. After WoW threw all that out for a menu driven quest interface, a lot of people are never going to go back to this style. I hate the menu driven system as I'm sure most of you do as well. It has lead to a completely useless PVE experience for most people who just click their way through quests to get to the reward. I hated it when it was first introduced in Baldure's Gate, but at least there you had choices that affected your characters development. Your quest log is a great step towards supporting the engine you have at least.
If you could create a really good dialog engine with NPC's, you would have something that would hold people here. No one likes to deal with an NPC that does nothing but tell you they don't understand. This will be a big challenge for you to overcome, and I hope you do it. I would suggest looking at some of the technologies in speech recognition as an assist, if you're not already doing so. There are some good tech's out there that may make the job easier. It will not be easy to do what you want. The amount of language you will have to support is staggering, but a good phraseology tree can go a long way towards making it a reality.
I will say as a newb here that I haven't experienced the RP police. I do my best to stay in character, but I'm still defining who that character is as I learn more about the game world. You have to give people that time to learn the world, but no one has come up to me and said I needed to roleplay better. That's probably because I am not in the higher end parts of the game. I would bet that most people do not leave because of this reason because they don't stay around long enough to experience it. They leave because the game is in alpha, and given what I've seen of the server and game so far, you aren't ready for a massive influx of players. You are about where you need to be for the game world you have. As it gets larger, the game gets better, you will grow accordingly.