I know there are plugins that cover this functionality, but why include another js file and write extra code? Why not build browser history management into the standard ajax method?

You could add a couple properties into the ajax method:

updateHistory - Boolean, defaults to false

historyHash - String, the hash to add to the url

There would also need to be a history init method that would load a url if a location hash exists on page load as well as loads triggered on browser back/forward buttons obviously.

This would take care of very simple ajax loads. The tricky part is keeping the flexibility that a history plugin has, since the developer may use location hashes that don't correspond directly to the url being loaded and also could require post or get data.