Yes, you have read the title correctly, the codebase of both WordPress (single user installation) and WordPress MU (multi-user installation) are going to be merged into a single codebase.
Matt, the founder and lead developer of WordPress has announced this news during his State of the Word speech at WordCamp San Francisco.
It is not clear when this merging will be done, but my guess is that they will be merged in WordPress 3.0. Once the integration is done, we can have BuddyPress for single user installs also.
This is great news both for the developers and end users and I am very excited about it. 
Excellent! Let’s hope it gets out fast!
@adam,
The latest news is that they may be merged in WordPress 3.0. Hope they do it soon