What do I mean? Well, I get addicted to specs. I find one that I like, and I stick with it. You might well be aware, if you read the Blood Sport columns I write, that I do a lot of PvP, but I also raid. And, the vast majority of the time, I do the same in both settings.
My shaman's talent specs are PvP restoration/PvE restoration. My priest? PvP discipline/PvE discipline (I'm in love with Atonement Archangel right now.) My mage? PvP fire/PvE fire. Are you beginning to see a pattern emerging?
So where is the problem in focusing on one talent spec for both your options? Well, take my shaman. I have thousands upon thousands of conquest points and valor points. I have full, epic-gemmed, Cataclysmic Gladiator gear. My PvE gear is all 397 or above. So when the raid drops and tokens come my way because we have nobody else to take them, what do I do? I play restoration in either PvP or PvE most days, and while I'd love to give elemental a go, I don't want to spend all my time respeccing. I would give ... I don't know -- what's an organ we don't really need? My appendix. I would give my appendix for a third talent spec. Heck, take my tonsils, while you're at it.
How about you? Would you use a third talent spec? Are you like me in sticking to one talent tree in two iterations? Do you long for more flexibility? Or do you not really feel the need for it? And, of course, why?