Verticals are where it's at these days, but as usual, if this thread was about something else like "hey, I want to use a vintage frame", none of this nonsense would come up. My very first Peugeot, came with fenders, horizontal drops, quick releases. No problem, and I was 12 or 13. My mom had a similar bike with wing nuts, though it was 3 speed. There wasn't any problem with consistent length, one just bottomed the wheel in the horizontal drops or the drops with adjusters. I don't know why verticals are better, I always assumed it was because it is somewhat more difficult, to hold a wheel to the rear while tightening the skewer, sorta a three hand job for those who have difficulties programing a VCR. Not something I would worry about in a world where one should be competent at switching out drive-side spokes.