I don't know any philadelphians that order with whiz either, and I'm a native, born and raised and still live here. My DH is from rural PA and he orders his with Whiz, but again, he's not from here.
I'm an "american wit", unless I'm at Pats then I'm an "American wit-out" because they overload the onions. I don't eat at Genos, because I just don't.
Never been to Dalessandros but they do have a good reputation, so I would try it out. One day I'll get my rear out there and try it. But these days I'd much rather have a roast pork with sharp provolone than a cheese steak.