The subject of the quote is Windows APIs (and is a pretty broad claim for someone who admits to not really having looked at .NET or C#…hmmm) but without taking sides on any technical merits I suspect people will apply the same trope to (MS/ECMA) Office Open XML file formats. And I think they would be dead wrong there: MS needs to enable their army of system integrators to sell MS back-end systems and Windows-based solutions in the new XML-ified, document-exchanging world. So MS is positioning Office as a platform that can both compete with web-based applications and integrate with them.
Think about it: Can MS compete with Windows versus Linux as a platform? Not really: you cannot get any cheaper than free… And can MS compete with Java versus .NET as a platform? Compete maybe but not win: they are a two-man conga line…But what competes with Office as a platform? Open Office? Err, perfectly good as far as it goes (I use it!) but certainly it doesn’t actually go very far (I am going to upgrade to the new Open Office 2.1 today…maybe it will solve the current problems I have with unusable arrowed lines and jaggy PDF export.)
The thing about XML is that it reduces role of the API to being glue for connecting declarative pieces: queries, XML documents, XML transformations, XML configuration, XML GUI. Worrying about crappy APIs is so 90s. (I don’t really mean that, of course. OK I do mean it a bit.)