Actually it's not even 60 Hz...
.... but something crazy like 60000/1001 Hz, because when they stared with colour TV (called color TV there) they found out their chroma sub carrier was interfering with their audio sub carrier. Instead of moving the audio, they simply changed the framerate.... which actually makes monochrome and colour TV in the US completely incompatible if you go by the specs. It also means that a show produced at a monochrome station will play slower at a TV station that already switched to colour... and of course computers here and there use 60 Hz straight.
And of course they use this weird scheme were they cut off part of their chroma sub carrier by bandwidth limiting their colour difference signals in weird ways... which gives them the ability to squeeze their image into 4.2 MHz... while PAL can be limited to 4.33 MHz, without having to resort to such a low subcarrier frequeny and weird trickery.
Biting the hand that feeds IT
