Kyle,
First you have to verify your numbers. Two out of 30 courses means that only about 1,066 of the available 16,000+ courses in the US allow walking.
Jim,
ALL the time, categorically no questions asked?
I'd say I'm pretty close in that regard. If there is any time where walking is not permitted, that's crap.
And if there is any time where I can't carry my own bag, that's crap.
So yes, 2 out of 30 is probably VERY close.
Kyle,
I've played about 30 courses here in Utah and not one of them "forces" me to take a cart. For two of those courses, you can insist on walking, and they might think you are crazy because they are insane walks...but in the end they will say knock yourself out, and let you walk.
In addition, having played at least 40 courses in California, and another 20 in Washington state and northern Idaho, I've only come accross 1 course that "mandated" taking a cart.
That is 1 out of 90 that made me take a cart.