Yes I think you are right, it has nothing to do with winglets per-se. Absolutely no passenger cares. (Except Qantas ones it seems, and they'll be back to 727s soon, the way they are going.!)
On the booking site when I get a ton of options and I want to be on the Biz class seat 737-800 with perspex barrier, how does Virgin show that on their booking site?