@Chip Bennett - Actually - it's possible to stay updated with beta and nightly builds. It doesn't come with core - instead you have to install the "WordPress Beta Tester" plugin - http://wordpress.org/plugins/wordpress-beta-tester/ .

It's not a big hassle to install the plugin and happily use the latest development releases(of course you can also use version control to directly update your core files with Git or SVN, but that's a different story).

I believe that this specific plugin should not be merged with core - if you're a developer and want to stay up to date with the latest WordPress builds - then you install the plugin. Normal users should not have that option out-of-the-box in my opinion.