My guess is (and I stress this is my opinion) that Totem manually create their transparent pngs much as @pumpdude48 does.For them to do it for every single photograph would be a huge amount of work.
@Number6I suspect you are correct but I haven't asked them.
By trial and error (more error than trial to be sure) I have figured out what works for me and have it down to the point that even a difficult photo only takes about 10 minutes to prepare.
I just wish they would turn the lighting down slightly to allow just a bit more border definition around the girls. The true blond girls tend towards very light skin pigmentation which makes the separation issues even harder and then like you mentioned, white clothes and shoes are a completely manual job with the eraser function.
It's a labour of love to be sure, else I'd have given it up long ago.