"When it was announced that WP would be a closed system Microsoft said that they would release a "business version" of the OS or some form of WP/WM that businesses could side-load apps on without having to release them through the market. Maybe I have some misconceptions here but that never happened to my knowledge."
I don't think there was ever an official statement like that, it was just a rumor that was going around at the time.
This was a few weeks after your post but thought I'd share:
"New Windows 8 App Deployment: Domain joined PCs and tablets running Windows 8 Enterprise will automatically be enabled to side-load internal, Windows 8 Metro style apps."