I'm not convinced that is true anymore. Since the FM band got stolen from Mr. Armstrong - it is inbetween VHF low and high and used to cause a lot of problems with analog TV tuners. Not so sure anymore with digital tuners and their advanced selection and rejection. FM used to cause a lot of "herringbone" interference on TVs during the analog days. With digital, it would just cause signal rejection (I guess). So far, I've tested at three different sites with 10 different antennas and four different amps. I haven't found any degradation yet due the FM band. That includes VHF low, high and UHF.
I can say for sure that at my place in NY - I get two RF channel 7s (Utica WXXA and Binghamton WBNG) and RF channel 6 (WRGB from Albany. They are all weak "fringe" channels and using the FM trap on the preamp makes absolutely no difference. The co-channel thing with two channel 7s is more of a problem.
In northern Michigan - same results. I've got weak distant signals for RF channels for 8 (WGTQ), 10 (WWUP) and 11 (WBKB). I also get analog channel 3 from Ontario, Canada (CICI). Again, they work the same with the FM trap on or off. But I do have all modern TVs. All my preamps have switchable FM traps. Channelmaster CM777 and AntennaCraft 10G222.