JSON is a very viable solution if I were taking data, say, from a database and sending that asynchronously to the client from the server. If I want to strip out sections from a page that is already formatted as XHTML, though, why go through the hassle of:
1. converting it to JSON on the server from wherever it came from
2. sending it to the client
3. converting it back to XHTML on the client
XML works well in these cases and has no additional processing costs.
I’m not an XML zealot by any means, but I like to have solutions for every scenario out there just in case it comes up. I understand where Markus and Tim are coming from.