Ha, I love how these threads morph! But yeh anyways, I'm in the Chicago area. My lot and the guy next to me have the 2 smaller lots on our road, around 2.6 acres. The rest of the lots around here are around 5 acres. We're all on hilly terrain, with yards that slope down into floodplains.
The landscaping crew is out there now, they're doing the house on either side of me, one across the road, and the property 2 houses down from here. They got 3 standers and a sitdown z-turn. Another crew that works the properties down the road from here has the same setup, 3 standers and sitdown z-turn. They're all on 52-60" decks.
Also, we just got back from walking our dog down a neighboring road...crews working there were all standers, no sit-down mower at all.
It's certainly true that standers save room on a trailer, so that's part of it. But, ask a landscaper who does this for a living what they prefer to use, what's more convenient, more comfortable, and less tiring...and it's a stander. I only mow my own property, but I could for sure attest.