Well they didn't bring over the entire game. It's just deathmatch and only the 'classic' maps that were played so much when Quake was at the top of the heap. The maps that are included in DMC play and look nearly identical to the originals. The maps that will be included in the first release are:

DM2 - Claustrophobopolis	[also a snapshot from original]
DM3 [2] - The Abandoned Base	[also a snapshot from original]
DM4 - The Bad Place	[also a snapshot from original]
DM6 - The Dark Zone	[also a snapshot from original]
E1M2 - Castle Of The Damned	[also a snapshot from original]

Exclusive? Yeah well it looks like there was a little bit of miscommunication in the PR department at Valve.