That's because in the UK (as in many other countries) universities get paid a fixed price by the government for each student they have, irrespective of results.
If they get paid based on real results to government specified tests they'd be more careful as to whom they admit.

It's the same here, but the entry requirements are high enough that most are never allowed to enter (several years more pre-university schooling than most kids get, at a higher level with more difficult tests).
As a result those kids that do make it are usually reasonably well motivated.

I think it will be very usefull if you take university regular classes. Internal assessments, seminars, assignments and other activities involved with the subject will give you better grip and insight on the subject. I agree with the fact that ultimately what comes is its your knowledge any way, gaining mastery over the subject is what is the ultimate satisfaction. Allso i would like to add that university degree will be an added proof which might help
you a lot if you want to use the knowledge as a profession(A must requirement if you want to play safe).

Try to take some team projects without consideration of earniing. You will learn and gain a lot.