zoomkat:, what I have found is that in the commercial and industrial sectors, the term "ROV" is universally used only to describe underwater remote operated vehicles. This seems to be a quirk of historical usage more than anything else.
The only time it is used otherwise, is typically in marketing literature, or by those who don't know the proper terms. I found this out in my own research, because I had originally termed the UGV I am building an "ROV", and I referred to such devices in that manner. As I was researching things using google, to see what others had done (using the terms ROV and "remote operated vehicle") I kept coming across underwater vehicles probably close to 99 percent of the time.
I continued to perform my research, and eventually found the definition "UGV" to describe my vehicle; searching on that yielded a ton more articles and information on ground-based remote operated machines. Further research at local libraries confirmed this difference in terminology.
Technically, I agree that it isn't right; in fact, I think there actually is a better term for underwater remote operated vehicles, but no one in the industry seems to use it to any great extent (from my research, it was in more common usage in the 1960s and 70s, then tapered off in usage to almost nothing afterward).
We are stuck with the terms as they are used, unfortunately...