In my experience, yes, the high-end IEMs that I've tried don't reproduce sound in all aspects as well as a good set of headphones. The IEMs I have now or used to have in the past few months are Etymotic ER4P, Klipsch X10, UE Triple.Fi 10, Westone UM2, Westone 3, and Sennheiser IE8. All of them have noticeable quirks that make them hard for me to fully enjoy, especially knowing that I've spent so much money on them. On the other hand, good headphones that I've had (actually most of the full-sized headphones that I've owned, including the SR-325i) don't usually have such quirks that really stand out. And the headphones cost LESS than the IEM. I actually think the $30 Koss KSC-35 I once had was more enjoyable than all of the IEMs above, but I can't confirm that since the KSC-35 cable broke after a few years and I can't listen to them.
If I wasn't concerned with portability, isolation, and headphone bands messing up my hair at work, I'd be looking at another headphone rather than messing around with IEMs.
Your experience may be different though, since your ears are different.