"It ignores features of HTTP that Netscape 4 supported in 1996, and mis-implements features of XML that Microsoft got right in 1997. It ignores 95 per cent of RSS and Atom and gets most of the remaining five per cent wrong."
Ouch. Because of this, many RSS readers are unable to receive feeds from the iPhoto. Unlike other standards such as CSS, RSS is not a centrally governed format. There is no real “compliance test” other than following the work of the creator of RSS. Apple refused a statement, and it may end up being left to the developers of RSS readers to ensure “compliance” with the iPhoto.