Where I work, we support browsers with over 2% of traffic, which means IE7,8,9, Chrome (latest), FF (latest and possibly 3.6 or something like that) and Safari (latest, IIRC, possibly latest + 1 older version.) The last 4 are largely the same, except for small bugs, and minor visual degradation is fine for the IEs. If your work requires you to support every browser, maybe you should start trying to build a case against that by making clear that requiring you to support every browser is a poor business decision.
But at some point, it becomes a zero-sum game. I believe this is what is happening with jquery: the amount of effort to support new features on older browsers (yes, that includes IE8) becomes less and less of an advantage. Hence their decision to compromise and support two versions of jquery, and have all or most of the new features implemented in the 2.0 version.