Discoverability needs to be layered. Come over and watch my Dad use your app. It's astonishing how much we take for granted.
With a recent project I watched a few totally inept testers discover all the features with no problems, but after launching it became clear that most of our power users were not discovering features. A quick bit of intro text and everybody is happy.
I think there's room for both, but I think it's nuts to assume that the people who really do need a walkthrough will:
a) Remember it
b) Be able to find out where to get the tutorial again, unless there's a giant "?" button at the top.
I think your vision is skewed, if all you require is "a quick bit of intro text". I've seen tutorials that are minutes long, and it's just awful.