I'm a little tardy to the party, but you're kidding me, right?
It's ridiculous that people bitch about the smallest things, especially when it comes to VIDEO GAMES.
I pre-order games most of the time because it includes some sort of mutual benefit, they get my money early, I get a nice privilege when the game is released, or something like access to a beta.
Whether it's exclusive content (like this, and I fail to see how that isn't fair, a lot of games make you pay for exclusive content, and this time it's FREE), an early advantage, or pre-order weapon packs like the Fallout: New Vegas packs/ Homefront's exclusive pre-order shotgun (and no one had a childish hissy-fit about the shotgun, did they?), it's nice to know that the devs appreciate my support. (Not that it's different from not pre-ordering, but everyone has the chance to pre-order. It's their own fault if they don't.)
I don't see why your actions should take away from my enjoyment. Name one over-powered pre-order weapon (in a multiplayer game, single-player doesn't count for obvious reasons) that have "broken" a game's balance.
I'm positive you can't.
Things aren't ever good enough, are they? This is
exactly why I prefer playing alone.

Gamers are some of the most picky and spoiled/self-entitled people on this Earth, it's no wonder we get a bad rap from the media.
"Some companies [are] withholding some content such as DLC to use as pre-order bonuses which prevent the people who don't want to pre-order from accessing them."
I fail to see why this is an issue, considering they have every right to do so. You buy the base game, everything that is on that disc is what you paid for. All else is extra content.