Your reading it wrong. "Data Connect - Day Pass" means just that, something that is valid for 1 day (with a 75mb cap) and then expires. It is not 75mb per day for a month, I can assure you.
Oh then that puts it in a new light.
Who the F#*% would pay $15/month just to use 75MB in a single day? There are free wifi spots all over the place why should I spill my wallet to AT&T?