Apple's page about Deneba's Canvas for Mac OS X

They mention OS X's Postscript-based imaging model a few times. Apple's always described Quartz as being based on PDF, not Postscript. Perhaps now that OS X is closer to release, Apple's not afraid to describe it as Postscript-based.

I think they were afraid to say Postscript or DPS because there was a perception that DPS was slow, and always would be slow.