A couple of quick questions just for clarification.

Are you referring to earphones when you stated "in-ear studio monitors", since I've never heard them referred to as "studio monitors" before?

Just which models were you looking at that you noticed such a wide variance in the ohms?

I just checked the specifications for the following eight "high-end" model in-ear monitors and except for the Shure Model E5C which has a rated impedance of 110 ohms, the impedance of the other seven models all varied from a low of 13 ohms to a high of 36 ohms.

Models:

Shure Model E5C (110 ohms)
Shure Model E4C (29 ohms)
Shure Model 500 (36 ohms)
Westone Model UM2 (27 ohms)
Ultimate Ears Triple.Fi 10 Pro (32 ohms)
Ultimate Ears Super.Fi 5 Pro (21 ohms)
Ultimate Ears Super 3 (13 ohms)
Etymotic Model ER4P (27 ohms)

What this the low ohm rating means is that all these earphones can easily be driven to comfortable listening levels by the output of most portable music devices such as iPods and other digital music players. Of course whether they will sound their best being powered by the relatively inexpensive headphone amplifiers used in most of those same devices is another matter entirely and the subject of much debate on places such as www.head-fi.org. I suggest that you give head-fi a visit since there's a wealth of information there on this and many other ear and headphone related topics.

I hope I answered your question.