I hate to break it to you guys, but the character voices we hear in the commercials aren't their in-game voices. If you listen to how they sound on the game clips we've seen, it doesn't match up at all. Commercials never use the original voice actors (they're often too expensive and too hard to get hold of for a 30 second spot). Their companies hire other actors or use voices from in-house for advertisements. Spyro and company may still talk, but until we see actual game footage of them doing so, we won't know for sure until we play it.
Yeah, Gill Grunt's voice doesn't sound anything like his actual in-game voice we've heard, and neither does Trigger Happy's.