I agree (yet again lol).
Because we aren't limited I have to go ahead and limit myself as a player with my current character. I'm currently a level 33ish Dark Elf full Assassin, finished out the Brotherhood and am on my way to finishing out the Thieves' Guild. After that... I don't want to do the Companions or College because it's not indicative of the character. I may not even do the main quest because the main quest is quite noble and a Dark Elf Assassin is well... not. However I may have to do some of the main quest so I can open up the tension between Imperial and Stormcloak so I can then play a Chaotic Evil role and join both, killing members of each how I see fit.
Great. That works for you. That's what's great about Skyrim, if you don't want to join the Companions or the College for roleplaying reasons, you don't have to. It's your choice. But there's no point in locking that content away from people who want to pursue it.
Like I said, I played a melee character, and I easily justified joining the College by the following. For one, every character starts out with basic magic. I wanted to learn more about this basic magic, so I joined the college (even though I was a melee-centric tank for the most part). Doesn't mean I can't learn about magic. I started as a student (very immersive), and before you know it, a crazy turn of events happened. The whole time I was completely immersed in the progression of the quests themselves. I felt like it all just felt "right". And it would have svcked if I wasn't able to join simply because I wasn't a primary magic user. After all, I'm the freaking Dragonborn, I'm special. I should be able to join any group I see fit.
And with the way the actual quests are written, it wouldn't have made sense to make arbitrary skill levels the sole basis of your advancement. Actions speak louder than words, and you were performing so important actions, therefore you advanced. Doesn't mean you need to be the end-all-be-all magic user, it just means you showed a lot of courage, a lot of initiative, and in the end you get rewarded for that.
You guys are assuming that people will play the game multiple times through. A lot of players just play once and what to see everything they can possibly see.