Ah! I was reading it as something about posting elsewhere, rather than about the way sign-ups and match-ups work. I have no particular preference either way. I do kind of like the flexibility to set up exchanges a different way when Google forms etc are used (and, as someone who hasn't run an exchange since she ran one on LJ and DW back in the pre-AO3 days, there's a certain nostalgia to it), but it's more work for the organizer(s), and I'm totally fine with the AO3 mold too.