I thought it was weird that they found that inner-ear had better bass response than over-the-ear headphones, but they did mention that could be an anomaly because the artificial head they use for testing forms a tighter seal with inner-ear headphones than most people's real heads would do.
The seal on a binaural head is likely a bit better than you'd get in real ears so inflates the numbers a bit. However, it's still expected to have better measured bass response from the IE phones despite this.
But, the frequency response doesn't tell the entire story in terms of what you 'hear'. For example you don't 'hear' much under ~60hz. What I mean is that frequencies below this are mostly not picked up by your ear drums but rather other senses feeling the pressure waves and your brain is wired such that it get's mixed into your perception of sound. The larger driver in CA headphones tends to activate the 'feeling of bass' more than in-ear headphones which can lead to the perception of louder-bass despite measurements favoring in-ear.
This effect tends to be more significant if you're listening to music with a lot of sub-bass, EDM for example.
I've found this to be true in practice though. I almost exclusively carry a decent set of sealing ear-buds for form factor reasons (they slip into my pocket) and the sound quality is just fine. Something about the way the little rubber inserts create a seal with my inner ear causes it to carry bass surprisingly well. When that seal isn't working (or doesn't exist, on cheaper hard plastic sets) the bass is nonexistant.
I suppose it's surprising because of the bud's small size, but then again, it doesn't need to drive that bass very hard either. That may help.
I guess I haven't tried enough earbuds to find ones that fit my ear canal well. I don't like the feeling of them inside my ears, so I stick to over-the-ear models.
