It's hard to know what Sony is up to, but I'm guessing that static thumbnail feature is probably for the PSP <-> PS3 connectivity.
They already had a video encoder for the PS3. They needed it for the Remote play functionality on the PSP. So it was just a matter of making use of existing work.
The thumbnail is also the start frame for your video clip. If all clips (mostly trailers) started at the start you would see a couple seconds of green disclaimer, then some black, then only a couple seconds of the actual clip. Thats why they did it. It's also just cool.
They already had a video encoder for the PS3. They needed it for the Remote play functionality on the PSP. So it was just a matter of making use of existing work.
I noticed when you playback a video clip there is now an option to choose a frame to use as the thumbnail for the clip.
Did you download those GTHD videos from the JP store or is that available in the US store?