This is an interesting phenomenon that I had thought would go away when Google replaced minimum bids with first page bids.
My understanding was that any active search words was eligible for display regardless of quality, but Google would estimate the bid that would be required to land on the first page. Obviously, this isn't always the case.
I'll try to identify some terms in my account that are experiencing something similar and see if I can get them to show by bumping the bid.
Thanks AWA. My question was mostly about why there are NO AdWords ads showing for such a common word, rather than why it wasn't appearing for my own ad. It's such a common widely-used word I would think it HAS to be used as SOME advertiser's KW. Is it OK to post it here?