It affects you in PvP.
You spend months getting very powerful, and then suddenly people get just as powerful in only a few days. While you ruled PvP situations, and it took parties of 5 to kill you, now all of a sudden it only takes 1 or 2 people to kill you. This can ruin your fun if you PvP a lot.
Then maybe you're not as good at PvP as you think you are and were just relying on gear the entire time.
In a PvP MMO, the "equation" should really be Numbers > Skill > Gear. Basically, a large number of enemy players should be able to take you down when you're alone, a much better skilled player in similar (or slightly worse) gear should be able to take you down 1 on 1, and when you have two equally skilled players the one with the better gear should come out on top.
Sadly, WoW fubared this right up from the beginning and gear trumped everything so that even the worst players imaginable could dominate in PvP simply because they were capable of raiding the top end content and anyone solely interested in PvP were left by the wayside. The Honor System attempted to fix that, but ended up being an even worse grind than any raiding ever was, so you were still better off tackling PvE content in order to PvP (unless you really had nothing else to do than PvP all day every day for weeks on end, or share your account). I quit WoW around Arena Season 4 because I was getting sick of lesser skilled players able to just crush me and some close friends just because their top end epics were far better than our mix of blues and "welfare" epics (just for the record, during the Honor Grind, I was able to get the blue Warrior set and was able to 1v1 almost anyone who wasn't decked out in 100% BWL gear).
Quite frankly, if you find that now suddenly people can get epic gear who previously were unable to and they're trouncing you in PvP I say "Good". You never deserved to be king of the heap, requiring "parties of 5 to kill you" because you relied on gear and now that the field is evened out a bit and skill is more a determining factor, your ego has taken a hit. Call me bitter, call me a troll, but I know a lot of people would agree.
~jaraxle