I'm not sure but I think a character needs goals to accomplish, even if it's a glass of water. He has to be natural and realistic for his age and time period. But there must be an obstacle or an opposing force attempting to stop this character from reaching his goal. He has to lose some battles, he shouldn't reach his goals or win battles too easily and he shouldn't be Mr. Perfect.
This character must have difficulty reaching his goals. He has to struggle, train and work hard to get what he wants. If he obtains the 'glass of water' without even trying, then that makes a sucky character.
It's interesting you should post this, because it blurs the lines between character and plot--which are really one in the same. You're right, that character could be the most real, human character there ever was...but if he encounters no struggle, the plot's a dud, and that makes the story a dud, too.
Like other posters have said, a well-developed character is one with personal flaws and conflicts but also virtues, one I can see in my mind's eye, all disembodied and new-agey and everything. When I care about that character's outcome, when I'll cry about it--it's a well developed character.
But it's hard to cry over a character who overcomes the external barriers with ease, like Blue said. Of course, you can always use skilled manipulation of the external as a point of contrast for internal conflict--but the conflict has to be there for a character and for a story to mean much of anything.
ETA: Sometimes I don't want a sympathetic view of a deplorable character. Sometimes I just want to be fascinated, also disturbed and even pushed to deep thought, by their horribly different perspective. For me, that's the appeal of writing a [an incestuously] sex-crazed, self-obsessed, hedonistic bitch, for me. Because...I'd make a crappy nymphomaniac psychopath, you know?? And I think most readers would, too. That's why people like to read the perspectives of people like Hannibal Lector.