Um… the average player pvp’s and raids in the same spec? Thats news to me and several people i know that are grinding rank. I think this is just pure conjecture based on your personal play style. I can tell you i know A LOT of people that farm gold to afford the respecs after the raid is cleared each week.
Examples - Shamans that pvp ele or enhance. They are typically forced to heal raids so this doesnt work for them. Locks who are DS/Ruin are strong when they can get a cast off, but ultimately they are very weak vs any other lock build. Warriors rarely pvp as prot even though they are prot for raids. Spriests - well … you only typically take 1 to raid so if u want to shadow pvp - respec there too.
I have spent this much already on respecs - doubt im an anomaly since i can name 6 people that are in the top 10% pvp that are as well.