I think you guys REALLY need a nerf. Your gear always looks freakin' sweet! It's not fair to the other classes that you guys always get to look like badasses when you come rolling in and shooting spells that look awesome! They need to hire little girls to design your armor for you like every other class!
On a serious note, I think that some of the complaining stems from frustration about class/spec changes. Lots of classes have had to put up with a roller-coaster ride of being strong to underpowered while mage has been pretty consistently solid (at least as of late) while also at times having more than one viable spec for pvp. Some classes only get one viable spec for pvp, and sometimes it's in a role you are not interested in. A few classes/specs are almost consistently at the bottom and don't seem to get the love from the designers that other classes appear to get. With as many classes/specs/abilities as this game has, there is sooo much to consider that it is inevitable that something will probably suffer somewhere and they will get things wrong. A few classes are just luckier (or quite possibly more important to the developers... bias is hard to avoid) than others.
Good control abilities are also pretty frustrating/annoying in general (almost by definition). They can really make you feel like you are unable to do your job. Nobody likes to have their character forced to take a stroll (slowed) during the middle of a battle while your target dances away from you while throwing spells at your face. Since mage is king of control, people (mostly melee classes) usually have to wade through a ton of it to get to you. I'm fine with control, but that doesn't mean the thought of going up against a team of mages doing nothing but controlling me all day doesn't give me nightmares...
It's also easy to forget that just because you can't beat a class, or a class shuts you down, doesn't mean it's the same for all classes. Each class has strengths and weaknesses (some more than others), so there is bound to be bad matchups. There are way to many specs and classes to have a perfectly balanced game. Every change you make based on a bad matchup will effect all other matchups for that class. People really just need to accept that your class will have bad matchups (unless the developers really mess something up, which happens sometimes, sadly, but they are usually patched). If you only pvp and tend to play without friends, it might actually be a wiser decision to base class selection on which matchups you don't want lose to, though things usually balance out when teams are involved.
This is all pretty much just stating the obvious, but I had nothing better to do at work today. Sometimes people lose sight of the bigger picture and need to step back and think about things before they rage sometimes...
Mages: Peaple get frustrated with you because you rock at control (which is oftentimes frustrating) and envy your class' consistently strong pvp viability.
All classes: You will have bad matchups, it happens, try to accept it and move on. If losing to a certain class reeeaaaalllly bugs you, maybe consider switch to a class that beats that class. It's also imposable to have a perfectly balanced game, accept that some classes will be stronger/weaker than others. Try not to take it out on other players, it's not their fault their class is strong.