When the iPhone uses XML it tends to parse it with libxml2, a GNOME library. This is a much newer (and thereby more functional and generally faster) version than the Apple one that comes on the iPhone.

2.6.32-5: applied all of Apple's weird patches to libxml2 "17.7.6" to make the parser fully compatible (fixing issues in App Store applications that were relying on broken validation behavior, such as Stanza)