Thats a good point, I didn't think of that. The FCC did make some allowance for low power FM transmitters, probably because they couldn't control it anyway. I see some people selling similar low power TV transmitters, but I don't know why it isn't more common. Since it is more complex than the FM transmitters and more of a risk, I wonder if the lack of FCC regs has stopped it in the US.

Low power FM refers to a specific class of licenses[1] and not the little radio dongles.

[1] http://www.fcc.gov/encyclopedia/low-power-fm-broadcast-radio...