Putting channels "offset" of their main channels is old school, cable systems across the country have done it for years, because of the severe problems with "ingress" on the cable plants. (Outside signals getting into the cable wiring). Theoretically a cable system is "closed", and in an ideal world, it is. No RF goes into , and the cable RF does not leak out. However any TV engineer can tell you, this isn't the case. Bad TVs, splitters from Radio Shack, people using twin-lead for cable tv, etc., can all cause these problems. The signal on the cable system will arrive at the TV slightly differently than the signal from the transmitter, so you get horrible beats, noise and lines in the picture. The signal from the transmitter gets into the cable plant, "beating" against the cable company's own signal. In Seekonk, for example, the old cable lineup at WJAR on channel 20 and WPRI on 22. As Jeff Lehmann pointed out the Newton cable system did the same thing, offsetting them. This was also why it was very common to see cable systems with nothing on cable channels 18-20 which fall into the public safety bands. In Great Barrington, there was a horrible problem with cable channel 19, which at the time was Sportschannel New England, where anytime the local police department would key up on 155.775, it would cause a horrible beat in the picture. You could hear the audio being picked up in the FM section during it as well. Cable companies also had ways to try and fight this style of interference as well, including using HRC (Harmonically Related Carriers) to offset the entire plant by +4mhz. With digital, VHF Hi ingress still exists, but instead of seeing beats, it looks like you have a weak channel. With digital cable, ingress causes the picture to just break up or drop out completley.
The other thing to note is usually where there is ingress, there is cable leakage (the cable signal "transmitting" outward)., and the FCC has very strict restrictions on cable leakage levels, due to the interference it can cause to public safety and FAA transmissions. Most cable companies (Comcast and COX at least do), have "leakage" patrols where vehicles literally drive around to detect this.