Because the 1X network is not fast enough. 1X is about 2x the speed of dial up and EVDO, if I am not mistaken, is 10x the speed. If you tried to download a video in 1X it would take an eternity and streaming video would be choppy as hell at best.

sprint doesn't seam to have a problem running streaming video over their 1x they do 15 fps and are able to stream live feeds

1x is 203 kb/s peek speed 40-70 kb/s real world speed ev-do is 2.4 mb/s peek with 400-700 kb/s real world speed.

but that is just sprint

so going by your answer v cast only works on ev-do?

V-Cast does only work on EV-DO. The phones will not allow you to access the V-Cast menus unless it is getting an EVDO signal. Once you have accessed the video and begun the download, it will still play if you lose the EVDO signal, but it is VERY choppy and re-buffers multiple times.

so v-cast is not streaming? it is a download that will play as you download?

No, it is streaming, unless you instruct the phone to actually download the video. However it is not streaming live TV. It is streaming pre-recorded video clips.