>That won't work with all browsers.

Well, for that matter, his choice of png images won't work on all browsers either. You have to draw a line somewhere :)

>Plus, it wastes a lot of bandwitdh, especially if the image is static

The code seems to indicate the image is a dynamic representation of current weather conditions that may not make sense to cache.

But yes, I concede that data uris do have drawbacks.