[robmcm]

It's great to know what a library like JQuery is doing under the hood, but if you are going about your daily development using a progressive enhancement to access the dom using document.querySelector you are removing support for IE7 for no real reason.

You can query the dom in IE7 using other methods and this is the goal of a library like JQuery.

Progressive enhancements are aimed at providing an alternative for browsers that don't support functionality, not that don't support functionality the way you want to coded it.