"We wanted to simplify setup and capacity planning, and enable federation across multiple farms. We also wanted to accommodate requests for integration from new partners such as Lync. Finally, we heard from many customers, both on Office 365 and on-premises, that they wanted the same improvements that our SkyDrive users enjoyed on a regular basis.Introducing Office Web Apps Server - | Office IT Pro Blog - Site Home - TechNet Blogs
To achieve these goals, we went back to the beginning and rethought how the Office Web Apps would integrate with other products now and in the future. We created a new model that separated Office Web Apps from any specific partner technology. Ultimately our model placed a relatively light coding burden on file hosts such as SharePoint while allowing us to run Office Web Apps on entirely separate servers.
This new standalone server product is Office Web Apps Server."
Wednesday, September 12, 2012
Introducing Office Web Apps Server - | Office IT Pro Blog - Site Home - TechNet Blogs
Microsoft more loosely-couples Office Web Apps and SharePoint; see the full post for before-and-after details