Good decision here by jQuery devs. The OP may not need IE6 support, but literally millions of corporate users stuck on IE6 *do* need support. Removing support prematurely would break thousands of jQuery dependent web apps across the web (using latest jQuery ver) for those corporate users.
And for what? It's not going to dramatically reduce the codebase, or make much difference to performance (as jQuery uses latest browser features where they're available, falls back to compat code where needed). As the team note, apparently IE7 needs many of the same fixes anyway.
Don't forget one of the primary purposes of jQuery was as an abstraction layer so developers didn't need to worry whether the client natively supported XPath queries, CSS3 queries, full W3C DOM2/3 support, etc.