At least their sound is unlikely to be tinny.
Seriously, though, my issue with in-ear headphones has been more related to comfort than fidelity, although over-ears have an obvious sound advantage because of their size. With all the earbuds I've tried, include the Shure Etymotics I had, I found that I had to push them well into my ear canal to achieve a proper seal, leading to discomfort and a constant awareness of their physical presence.
Well said. And I agree completely with you.
On the topic of in-ear head-phones, the issue of comfort has been my major concern as well; not just a feeling of discomfort, bout occasionally, veering into actual soreness.