We've been to plenty of campgrounds that have no WiFi at all. Of the half dozen or so public campgrounds we have been to in the last 2 years we have only found WiFi at Stone Mountain Georgia's campground. Their wifi was reliable and it is monitored, like DSL speeds. When we were at TopSail Hill SP they boasted they had WiFi, but it wasn't usable at our site.
Probably about half of the private campgrounds we have visited have some form of WiFi. In most cases it is only available down by the office or some centrally located area.
Fortunately, our seasonal campground has good wifi. It is monitored, but they are pretty generous. The speed is good and they have not hassled me even though my router reports that we have used an average of about 8gb/month over the past few months.
-Michael