Tabs requires ui.base.js?

Tabs requires ui.base.js?


I see on the wiki that Tabs now requires ui.base.js. (http://
docs.jquery.com/UI/Tabs) This seems like a large requirement as the
packed version of tabs is around 6.5k, and the packed version of
ui.base.js is 3.7k. Looking at the current base file (http://
dev.jquery.com/view/trunk/ui/ui.base.js) it seems just about
everything in there is related to mouse stuff.
So what functionality is in there in ui.base.js that Tabs needs that
warrants a 50%+ increase in filesize, as well as an additional
connection to the server for the additional file?
I'm sure I'm missing something obvious.
Aaron