1: Lots of companies will reject you on sight without a degree. I don't think it's a good thing, but it is reality.
2: With a degree your ability to move overseas dramatically improves. I moved to America after graduating. I flat out couldn't have done that without a degree. Points based systems immigration systems like New Zealand have dramatic bonuses for people with degrees.
3: You don't have to jump through the hoops and explain why you don't have a degree all the time. Stupid reason I know, but it's something I've seen friends without degrees have to do constantly - and not just in career situations. As I mentioned, I went to a no-name university. If you live in NZ, you'll know it. If you're an American, chances are, you've never heard of it. But because I have a degree, it doesn't ever really come up.
4: The cost isn't that bad, when you spread it out over a career. My degree & living costs cost about $60k NZD (~$40k USD). That's $1k USD / year, or $.50 per hour. Considering how my income has multiplied in the few years since I've graduated (SF wages help tremendously here), the actual cost is barely anything, even when you control for the opportunity cost of studying.
Where I think College returns make a lot less sense
• Paying out of state tuition for lifestyle reasons, when you're going into a relatively low paid field afterwards (e.g. teaching).
• Paying private school tuition at a school without a strong reputation
• Grad school, in general, seems to be a rip off