The move was not a total surprise: Two weeks ago, screenshots of a leaked copy of what would become Windows 8 Release Preview showed Flash present in the Metro edition of IE10.

on Thursday, the same day it launched Release Preview to the public.

In some respects, the bundling of Flash contradicted that it would not allow plug-ins for IE10 on Metro, including Flash Player, in either Windows 8 or its ARM-based offshoot, Windows RT. Many Windows observers, however, gave Microsoft a pass because Flash was technically not a plug-in, but was instead baked into IE10's code.

Last September, when he announced IE10 on Metro would be plug-in free, Dean Hachamovitch, the company's lead executive for the browser, made this argument: "Running Metro style IE plug-in free improves battery life as well as security, reliability, and privacy for consumers."

Four days ago, Hachamovitch didn't mention last year's promise other than to repeat that IE10 on Metro will be free of plug-ins. "The Metro style browser continues to provide no support for other separate ActiveX controls or plug-ins," said Hachamovitch.