[jmileham]

I wonder if there's any effect that in-ear headphones are cheaper to produce but have advantages in accurate low frequency response?

Of course all this is confounded by the fact that music will tend to sound best on speakers/headphones with a response curve most like the speakers/headphones that the mastering engineer used (or more accurately, the set of speakers/headphones that the engineer compromised among). You will probably tend to have the best experience listening to music with the popular devices within a given musical subculture, because mastering engineers will be targeting those devices.