I think most of them are field dressed, you just can't see it. Some people field dress a deer differently. Some just cut a small opening and pull everything out of it instead of splitting the pelvis and really opening the deer up. This is how I was taught to do it. I trim around the anus, remove the sexual organs then slit the windpipe at the throat. Then I make a small incision under the breast bone. Big enough to get both hands in. Then remove the intestines. After that I cut the diaphram reach in side and remove the lungs, heart and windpipe. It's not quite as easy as it sounds, but it works and very little meat is exposed or touched.
Some processors will the gut the deer for you for a fee though. Maybe that is what some are doing. I don't think it's that big of a deal if it's cool out and you get it there in a timely fashion. If I shoot a deer in the morning it is usually at the butcher that day.
Like you guys though, I field dress the deer where it lays usually. It makes the them lighter to drag
Paul