User blog comment:Tage103/Sonic Heroes is a dreacast era game now?/@comment-477304-20120506233139

None of your reasoning that Sonic Heroes is a Dreamcast game makes any sense.
 * 1) The game may call back to the Adventure duology, but Sonic Adventure calls back to Sonic the Hedgehog 2, Sonic CD and Sonic 3 and Knuckles and that's not a classic game.
 * 2) Yes the CGI is better in the modern saga, but that's because those games run on next-gen consoles, of course they're gonna have better graphics.
 * 3) Sonic '06 didn't get new VAs, Shadow the Hedgehog did and the most of the cast got replaced again in Sonic Colours, which is a Modern era game so the different VAs argument makes no sense.

So in short, Sonic Heroes is not a Dreamcast game, it is in the Dreamcast era because, well, word of God, but the most likely explanation is to make all eras equal, it's not a big deal anyway because the names are never brought up in game anyway.