Yes, Gravity Forms has a date picker field and it actually uses the jquery ui datepicker you used in one of the examples you referenced.
Whoops, I didn't even notice that :) I created a new form with a date field but I didn't click the actual input field. I think I was used to seeing a little calendar graphic off to the side.
My bad :)
Yea, in a future release we plan on making it an option to display a calendar icon to the right of the field. So I can see how you may have missed it.