My Cube has a Digital Out port. How else would I have described what one looked like?
And yes, if you really wanted Progressive Scan on your Cube, there wasn't a lot stopping you. But Nintendo seemed to be constantly trying to present this image that the GameCube was unsuitable for higher-end entertainment centers (see the lack of DVD and Dolby Digital support), they made you jump through hoops to get the component cable, and then (while cutting the rarely-used port) they flat out told us that more than 99% of GameCube owners didn't want Progressive Scan.
The idea of the Rev supporting Progressive Scan, and only Progressive Scan (as in, no S-video or A/V cables or R/F switches) is amusing because of that previous stance. Of course it's obvious that those Rev prototypes were ProScan-only because they wanted the Rev to be seen (by whoever they were showing it to) in it's best possible form, while they tell us about the next thing that we apparently don't want, which is HD.