that many players are already switching

Bashiok, one of the issues is that many players are already switching specs on an encounter by encounter basis. This is already the norm. If you don't want that to occur, it's too late to stop it. Having more than 2 specs just means that you aren't limited to just PvP and PvE, and you can keep up with the players who already have 2 PvE specs.

Tanks already have to cheap wow gold switch to a dps spec for one tank fights. Hunters already switch pets based on the needs of the groups, which is akin to respeccing. Healers already respec to dps when there are too many heals in the raid or when it makes sense to have fewer healers based on fight mechanics. Rogues already change their weapon poisons based on the encounter mechanics.

The fact is that encounter min/maxxing is already the norm. Making respeccing time-consuming doesn't change that. It just makes the process more annoying. Having the ability to tailor your character to suit the encounter, if anything, enhances the depth of the play, because we have to make meaningful decisions about each fight.