I think you are creating a straw man question as the overwhelming majority of partners have open sourced most/all of the applicable code. Take a look at http://www.ironfoundry.org for instance from Tier3 who has taken a very liberal approach to open source with their Cloud Foundry based service.
Appfog has also contributed back their code for PHP to Cloud Foundry. They are doing a very nice job of expanding the potential deployment targets as one of their competitive advantages (HP, Joyent, most EC2 regions).
Thus to answer your question I've seen robust contributions back with a very liberal amount of open source code, and a focus on value-add through service delivery options.
I'm curious about your view of the hybrid deployment model many of our users prefer with an on-prem instance that can be deployed to multiple service providers.