Google Page Speed does not think Google Adsense javascript is optimized for caching.

Today, by chance I ran Google Page Speed Firefox on one of our sites with Google Adsense.
Strangely enough, Google seems to think Google AdSense for search is not optimized



Obviously caching of Ads would not be really useful but should not Google Page Speed analyzer know better ? Or Should Google AdSense for Search specify a proper expiration tag?