In this case, looks like they took secrecy over compliance. Instead of asking someone like Winer (who would gladly hold his tongue if it's to promote a standard instead of break it), as there is no standards body for RSS, Apple just kinda forged their own standard. Yeah, it uses standards in the same way I use the military: I'm glad they are there, but I never joined up. Basically the RSS is so screwed up the only way to read the feeds is to use Safari.
The full details of what is broken is over at this unofficial documentation of iPhoto 6.0 photocasting feeds. Dave Winer has his words, witty as always, and Kevin Yank winds up saying what some are thinking: "Apple is the new Microsoft." Although I would like to point out that that unofficial documentation goes to Apple lists, and I have a feeling they are going to look at this. Heck, they might even fix it! So next year I'll gladly pay another $79 for XML that "just works."