The XML Schema for Keynote 1.0 was not actually developed in house; rather it was designed by a set of highly knowledgeable contractors. For the second round of applications (including Keynote 2.0), the XML Schemas were brought in house to Apple and this is where the headaches started. The schema was changed on an almost daily basis, breaking builds and causing mass amounts of confusion and bitterness. Also, by bringing it in house they lost the use of all this XML expertise that they had for the first version of the file format. There was no thought to standards or conformance at all. Rather they authored the schema in an ad hoc manner to suit their in memory file structure.
To sum up: the second round of file formats were constructed by amateurs.
Sad but true.
Yes very sad! Apple needs to put a little more effort into its file formats like they do with products.