Nintendo fans: "I'd rather have good games than good graphics" Wii U comes out "Alright HD!!!, I'm sure without a doubt in my mind it will be just as powerful as PS4/NextBox!" "No such thing as casual games, what constitutes as hardcore anyway? Bullets and blood, yeah real hardcore >_>" *whines when they don't get good third party games like GTA V*

Microsoft fans: Think it's okay for Microsoft to show a bunch of celebrities, guest speakers, multiplat games, kinnect/casual stuff/ and timed DLC and pretend that Microsoft always has the best conference. Pretend that Gears and Halo are the holy grails of the gaming world and that no Sony exclusive interests them. Say FFXIII would have been a let down either way. Act like Microsoft caters to the core gamer.

Sony fans: Think every new PS3 exclusive will be the best thing in the entire world, until a new exclusive comes along that is. Blame Microsoft for the FXIII let down. Say all games for other platforms are casual. Act like Move wasn't a total failure.

Nintendo Fans: The belief that they don't want Nintendo M rated 1st party games....when they secretly do.

Sony Fans: The belief that only 1st party exclusives matter. Multiplats, downloadables, and motion games do not exist

MS Fans: The belief that all they need is Halo and Gears.

Nintendo: If it's Mario, it must be good!

Sony: If it's a new IP, it must be good!

Microsoft: If it's an FPS, it must be good!

The following is not meant to be taken completely seriously (like everything else in this thread).

Nintendo Fans: Tragically blinded by nostalgia. Even when Nintendo does something to please their dedicated fans, it's just not as good as playing A Link to Past on Christmas when they were children and blah blah blah blah blah. No wonder Nintendo is trying to create new fans.

Microsoft Fans: There are Halo and Gears and Fable fans... but Microsoft fans? Never heard of them.

Sony Fans: Perhaps the belief that "mature" gamers only care about games that are very artsy or impressively cinematic is a good one to focus on. A shame considering how previous generations of Sony games were so excellent at pure gameplay that they didn't need to have massive budgets in order to succeed. Sigh. It's very telling considering how Sony squandered the opportunity to make Demons' Souls into a first-party IP. That game was about as pure and hardcore as a game can get.

This, and also many other answers, and all the ones in the first page of this thread.