My vet back East felt that with the convolutions she observed in their ears, the inner ear canal was more narrow, with poorer air flow...and many (not all) Curls do produce a dark brownish wax (which many vets mistake for ear mites, when it's not). Breeders advise pet owners to make checking their ears once a week, part of the grooming routine...but stress it is very important, not to try swabbing down into the ear canal...using a cleanser such as Nolvasan Otic should be by moistening a q-tip and swabbing the outer area of the ear. Signs of an infection or problem to consult your vet on are reddedned ears, lots of head shaking or pawing at ears, "swishy" sounds when they shake their head...a lot of which also sounds like mites, but in Curls, usually just means they've got a wax build-up and/or infection..yeast is one result I've seen.
Then there are variations in tightness of the Curl, ear height and width of ear base. One goal for breeders of Curls is for a nice wide open ear base.