Do you not remember the Xbox 360 announcement on MTV??
E3 is much bigger since that. After the Wii hit every E3 has had all main stream media covering it. The MTV event was a forced thing to get attention. That no longer is the case a 2 hour prime time slot for free with the whole world watching and covering it. If they were to do a MTV type of show make much more sense to do it a month before launch to as a last sales pitch and launch into the major ad campaign.