In thinking about this topic, I really had to do some introspection about how I am as a gamer. Am I the type of gamer that wants to see every level, so I simply put the game on easy mode to be able to burn through a game in a couple nights? Or am I more of the type that wants all the bragging rights because I've beaten a game on ultra-extreme tough mode?
The answer is: It varies with every game.
A lot of games, I will simply play through on easy. If I enjoy the game, I'll bump up the difficulty so that there's more of a challenge. If it gets too insanely difficult though, I'm out. Some games will unlock additional content or levels if you play the game on these more challenging modes though.
Take the Guitar Heroes series, for example. (Hope I remember the skill levels here.) Easy is good for people to start learning. But I enjoy music, and I've played guitar for a few years, so in short time, that level got quite boring. Medium is a bit more hectic, but with practice, most people can probably do this level. Hard is where the boys and men are separated. You have to put in some practice to be able to move your fingers around now. And Expert? Well, that's just insane. Maybe that's what separates the hardcore from the casual. lol. When I was playing Guitar Heroes, I generally played Medium/Hard. (Once Rock Band came out, I haven't purchased any more of the GH series.) I really saw no point in getting a finger cramp from attempting Expert.
Rock Band, on the other hand, didn't make the difficulty quite so rough, in my opinion. With practice, I think most people can do Hard, and Expert is simply knowing the "real" song. I generally play Rock Band on Hard/Expert. The difference is attainability.
Well, I played both those games and skill levels for my own personal satisfaction. I don't play Expert on songs to show off amongst my friends. No, I do it because it makes the game more fun when I have to struggle a bit. But there's certain solos that make me want to simply restart the system... oh, and I fail almost instantly on those.
Now... what the heck does that have to do with 10-man and 25-mans? First off... they're not equal. It's more difficult to do the 25-man runs, so you get better loot. I would expect that. But I would also expect your options to be the same (which they're not). So, if you get a trinket in 25-man that increases your spell power by 111, then you should be able to get the same trinket in 10-man that increases your spell power by say... 98. But that's just not the case.
Naxx loot has 4 trinkets for 10-man and 8 for 25-man. Furthermore, not all classes can get 2 legitimate trinkets from them. Like what would I do with the second ranged DPS trinket from Naxx as a mage?
Anyway... the whole point is that I've starting asking myself: do I care? And if I do, why?
I've made fun of a buddy of mine because he's still in mostly blues. I've suggested a few upgrades, even crafted ones, but the cost simply doesn't justify the upgrade. And he does pretty good DPS. He obviously plays his class well, but he just doesn't devote that much time to raiding to be able to get full epics.
And the whole point of the game is that I want to have fun. I want to hang out with my friends. And maybe every once in awhile, I get a gear upgrade. But mainly, I want to see the content, or... I want to finish the game. I think because of TBC and original wow, I still have this leftover mentality that I have to be in 25-man raids. But really... I just don't care that much. Furthermore, I'd be perfectly happy if I was simply running 10-mans with my 9 closest friends, and hopefully somebody (doesn't even have to be me) gets an upgrade.
So don't let the mob mentality make you do things you don't want to. It is a game, so make sure you're happy while you're playing it. Do what makes you happy.
p.s. If running 25-man content makes you happy, then by all means... go for it. This was in no way meant to bash or discredit anybody else's idea of fun.