Some nerfs come about due to PvP, but saying that all or most would be a flat out lie. Read through the dev notes on PTS and patch notes. The vast majority of changes are made due to under or over performance in PvE.
I also do know why the forums are so divisive. Seriously stop trying to force a wedge between PvP and PvE. Many players do and enjoy both. Even if they don't, they are still playing and enjoying the same game. Let them have that, even when it is passionate about things they don't like. People speak up when they care.
Edit: In the end changes are the devs call, not the players. There are mountains of things that get ignored and go unchanged that players want. Stop taking changes out on each other.
The vast majority of changes are made due to under or over performance in PvE.