I was playing with Google Finance today, initially looking at that outstanding dollar value of Google's stock, when I noticed someting.

Inside of the historic data part of google finance, where you can view historical prices, you can also download them to csv.

The url is as follows:
http://finance.google.com/finance/historical?q=NASDAQ:GOOG&output=csv

Now I changed this to xml, and for me at least it didn't throw out an error page nor show a normal page, it just returned blank:
http://finance.google.com/finance/historical?q=NASDAQ:GOOG&output=xml

Same thing happens for JSON:
http://finance.google.com/finance/historical?q=NASDAQ:GOOG&output=json

Now however, if I change that to something like txt, doc or even html it spits back a normal page:
http://finance.google.com/finance/historical?q=NASDAQ:GOOG&output=txt
http://finance.google.com/finance/historical?q=NASDAQ:GOOG&output=doc
http://finance.google.com/finance/historical?q=NASDAQ:GOOG&output=html

Perhaps they're just waiting to flick a certain switch?