If that were true, an unlocked phone should cost less per month in subscription fees since it is not being subsidized by the carrier. No US carrier does this.
If I want to buy a new phone I can either pay full price for an unlocked one, get a small subsidy to lock myself to a carrier for 12 or 24 months, or I can get an even bigger subsidy by paying an increased subscription price for 12 or 24 months.
As an owner of an unlocked phone, that would be awesome. It's probably still very uncommon to buy an unlocked phone though, and the carriers don't want to give up money. As it grows more common, maybe I will get to see that day.