"240Hz" is only for HDTVs and it only refers to internal video processing for smooth playback of video. The same also applies to 120Hz HDTVs as well.
HDTVs only accepts 60Hz input and operate differently from 120Hz PC monitors. Specifications for TVs and monitors are developed by at two separate entities. Maybe in the future these entities will consolidate into a single entity to develop standards due to convergence. However, this is very unlikely.