Yeah, with classes (Oblivion style), he'd have "mastered all the combat skills" and then be at level cap (since only the class skills would advance you). So he'd still be unable to "advance" his character any further.

I was only replying to the bolded part (I should've made that clearer):
to gain more levels and be able to confront more powerful enemies and find better loot, he has to become a mage and a thief.
With classes, only a few select skills would affect your level, instead of all your skills.
[Directed at Donchochino]: As for advancement in individual skills, there has to be an end somewhere. Yes, it's sad to see your Blade skill hit level 100 and know that your warrior will never be able to improve his Blade skill again. But the alternative would be no caps, and that would lead to unbalance.
Personally, I don't see it as a problem, but then I'm not as focussed on "advance the character". If I've maxed out the skills I chose for a character, then she's "done" advancing that way. So I don't feel "forced" to use another playestyle. Personal opinion, of course.
I don't feel
forced either. I do however feel very encouraged. My leveling in Skyrim on my main character slowed down to a near-halt around level 50. I wouldn't have went over level 60 if I hadn't changed playstyle. But there were 30 more perk points for me to put into a skill of my choice! Of course I changed playstyle and tried to max all skills. It's like dangling the Citadel-charged version of the Gravity Gun in front of my face when in Ravenholm in Half-Life 2. Of course I'd pick that one over the normal Gravity Gun!
My biggest gripe is that with the DLC adding more perks and new creatures that only appear at high levels I'll have to level up in things inappropriate for my character. The new perks aren't so bad. I can make a character specifically focused on being a vampire or werewolf but to see legendary dragons Vriddi would have to start using skills that just don't suit her.
This is one example of the encouragements to level up. To see a Legendary Dragon (there's even an achievement for killing one!), you have to level up to level 78, which forces you to level a lot of skills, many that you probably don't even want to use.
It's the same thing with Guilds. Nothing stops you from joining every single guild and completing them, and you will only be rewarded for doing so. You can choose not to join all of them, but the game encourages you to do it - the main quest forces you to join one (not really, but unless you possess Force Precognition it does!), and another quest cannot be completed without interfering with two of the "guilds".
And Star Wars was apparently bought by Disney today. I feel like aquiring an Akaviri Katana and commit seppuku.