"A character is only as intelligent as his player." Not true. There are so many ways this could be represented. As a short example, let's say you play a barbarian with low intelligence. You get asked a hostile question. The only response you character is allowed to make is "Die you son of a dog!" If he's got REALLY low intelligence, the player may not even have the option of staying silent, and the character will automatically respond that way. If you played a smarter character, or a character with better Speechcraft, you would be given more options, and a REALLY smart character would even inform the player what response would yield what result. (Yes, Speechcraft is a skill which in some cases would negate the need for Intelligence...but the Intelligence (and Personality) of your character would determine how high their Speechcraft could be. That's the relation between Skills and Attributes, and frankly, I can't imagine an in-depth RPG without it.
Intelligence does not necessarily affect speechcraft. That's why there's a skill for it. I'm an intelligent person, but half the time in a face-to-face conversation things like "Die you son of a dog" is all I can come up with. I've known many people who can create rousing speeches but wouldn't know how to tie their shoe without Youtube how-to videos.
As far as assigning arbitrary numbers, your "strength score" is how many pounds you can lift in any given exercise, your "Speed score" is how fast you run a mile in a minute. While they are compressed into a scale of 1-100 for the purpose of the game, they represent traits which certainly can be quantified specifically. And as you said yourself, we measure Intelligence with IQ scores, SATs, etc. Those are probably the least accurate tests, like using benchpress as the only metric of strength, but they give a general idea.
I don't know what I bench press. I also know that being able to bench press more doesn't necessarily mean I could punch harder than someone else. It's a different kind of strength. Speed is obviously distance over time, I can't refute that (nor would I want to), but a typical person won't assign a number to themselves and say "That's how fast I am". They might know their fastest time if they play sports.
I guess if I want to generalize my point, the things attributes govern don't need numeric representations, because the things they govern are not static and one-dimensional.
Of course Beth has already made their decision, and most people are fine with it. And I'm sure they did a great job of making a fun RPG without it. However, I really cannot imagine a mature, complex, and in-depth game without attributes. Not quantifying those numbers really limits what you can do, or at least how you can do it. For example, many people want to be able to drag bodies. We probably can't, which is it's own issue, but if we can, would it make sense for a rail-thin Wood Elf to drag the body of an armored Orc as deftly as if the situation were reversed? And would a "Corpse Disposer" perk really fill that gap? How long before the Perk system (which is GREAT for SOME aspects) becomes more cluttered and obtuse than an Attributes system?
I make no connection between attributes and "mature" or "complex". The perk system is, in pretty much every way, more "complex". Were they to fix Oblivion's attribute system, it would be more "complex". I don't see what's mature or complex about increasing a number to make a character perform marginally better. Skills and perks do the same thing, just with fewer numbers between the game's variables and the player.
In response to Omega's first sentence above yours: Yes, I know the game is based on numbers. You might have realized that if you read my post. Attributes are only a representation of changes to the game's lower level variables. Those same variables can (and will) be changed without the old attributes. You are bemoaning the difference between two book covers, when the contents read the same.