Actually, what's misleading is the title to this thread. By your own admission, the hotel did have free internet so their description wasn't misleading in the slightest.
I understand you were a little peeved but why oh why do people have a problem accepting responsibility for their own actions or inactions???? If you can afford to pay $190+ for a night then $5 for the convenience of not having to find a store selling the same cable is a bargain.
It seems like the more expensive the hotel, the easier it is for them to nickel and dime. The clientel that stay there generally don't mind paying what amounts to nickels and dimes for the convenience of things like ethernet cable.
And it seems that it is a "full-service hotel" as they were able to sell you something that you forgot at a very reasonable price.
You don't like the fact that they didn't provide it for free. That's fine, but don't slander the hotel.