Caching of the standard style sheets should be longer, at least two days. This makes it score better on Yslow
Fixed in 1.9 and HEAD.
In 2.0 or later:
1) THEME->csslifetime lets themers adjust the cacheability of their theme in seconds, except:
2) In dev mode, caching is 60 seconds all the time.
3) Standard theme always has a long 2 days