Is this standard practice when opening a product up to feedback from users? It seems like they get full ownership of everything.

From their TOS when registering for the "Insider" program:

You may provide code, content, comments, feedback, suggestions, information or materials via the Program Services ("Submission"). By providing a Submission, you are irrevocably granting Microsoft and its affiliated companies the right to make, use, modify, distribute and otherwise commercialize the Submission in any way and for any purpose. You also give to third parties, without charge, any patent rights needed for their products, technologies and services to use or interface with any specific parts of a Microsoft software or service that includes the Submission.

From:

http://windows.microsoft.com/en-us/windows/preview