Criminal Hacker gets Dev ID, makes malicious app, distributes said app, runs for months, then one day whamo! it does Nasty Shit. Apple blacklists the app and the Dev ID certs. Easier worm and virus control. At least until one of these rogue devs finds a privilege escalation bug that gets it out of the sandbox and also into more privileged execution.
It's not a magic bullet, but it'll be a good thing unless they abuse it. An example of Apple's track record in this regard would be GPL apps on the App Store - they'll pull the app from the store but I have yet to hear Apple 'remote wiping' someone's previously downloaded apps.
Tangentially, I'm a little miffed at spending $100 to get certificates to do Developer ID, but in the Grand Scheme of Business, it's just not that much money.
*I have flashbacks to 'The Net' - I shudder