Re: 60Hz vs. 120Hz vs. 240Hz TVs
That's what I would think. There might be some ever so slightly noticable differences in terms of motion but, in practice, no. For as long as the input is limited to 60hz then any differences are always going to be artificially made as a post-process.
Keep in mind that LCDs don't actually refresh the entire image like CRTs used to; the individual crystals simply change state. The reason why 60hz was 'enough' for so long was because they don't flicker like CRTs. If it weren't for 24fps films then all these 120hz sets without a 120hz input would basically have been pointless, and I think the main reason that manufacturers implement these frame interpolation technologies is to justify that.
Some people do claim that 120hz can reduce motion blur on a 60hz source but I can't say I've noticed it myself. I would imagine it's just the frame interpolation at work.
It's better to be dead and cool than alive and uncool.