That's really true. A lot of anime voice actors never really "change" their voices from role to role. And if they ever do, the changes are reallllllllllllllly subtle
Steven Blum, for example, sounds different as Kazuma, Spike, Shishio, and Roger Smith. But you can still tell it's him. He just changes his tone slightly or something.
If Gaara's voice is in fact whasshisface who does Brock, I hope he sounds damn evil and is able to pull it off!