A trailer showcasing animations doesn't make for very good viewing, especially not for a first reveal. Was it a normal cop chase? No, every entity involved in the pursuit except the player was spawned by and was under the control of LSPDFR. GTA V doesn't dispatch the police buffalo or police cruisers in ambient chases. It also doesn't dispatch additional units to the chase either.
Voiceovers? No, all in-game audio. Some of it from the AI, some from the player.
Is it, all in all, fairly basic compared to LCPDFR? Absolutely, but what do you expect merely two weeks after the game was released?