I can think of one situation where having a given maximum response time would be necessary; viewing "3D" content using (currently LCD) shutter glasses. In order to use this technique, where the left eye image is displayed while the right eye is blinded and vice versa, the display has to be able to completely change images over the whole frame at twice the desired frame rate. Twice because you need two images for each frame; one for each eye.
For 30fps you need to change the image 60 times per second which is once every 16.7 milliseconds. The time to switch frames should actually be much shorter than this because the frame must be switched and stable before you can switch the eye shutters.
The sequence would be:
1. Open the right eye shutter while the diplay is showing a stable right eye image.
2. Close both shutters while the display is transitioning between the frame's right and left images.
3. Open the left shutter.
4. Close both shutters while the display is changing to the next frame's right image.
5. Repeat from step 1.
The response time of the set dictates the length of steps 2 and 4. You obviously want to keep this as short as possible in relation to steps 1 and 3 because neither eye is seeing anything during the transition time. So, for alternate image 3D content viewing, the faster the set's response time the better, regardless of the length of retinal retention.
At 30fps, 2ms response might be ok, or even 4ms if the set was bright enough. Note, though, that quoted LCD response times are somewhat like quoted contrast ratios. There are various ways of measuring them and the manufacturer will generally use one that sounds the best. The actual time from one fully stable image to a totally different fully stable image is probably longer than the response time specified. Here's an article that talks about this:
LCD Televisions and Image Lag
Whether 3D capability is a desired feature, that would help sell sets, is debatable. I can see it being an interesting feature for video games. The recent release of the movie "Beowulf" in 3D indicates that there could be some interest in having this technology in a home theatre.
It's unlikely that current LCD TV technology could handle it. Plasma may be able to do it. DLP, with its 16 micro
second response times, can handle it easily, and Samsung has included this capability in some of their current DLP RPTV sets.