We are already working with the Dryad team on a version that will not require Windows HPCS. We had to make a decison early in the project whether to leverage HPCS for the initial implementation or base it on Windows and build the necessary scheduler, monitoring
utilities, and file metadata management. The decision to start with the HPCS implementation was to get Dryad released asap and we can deploy this on HPCS clusters that he have set up at universities worldwide. And since Windows HPCS is free
through the MSDN Academic Aliance, this would not cost our academic partners a dime. All in all we thought this would be an effective way to get started.
As for the choice of license, our group in Microsoft Research is responsible for university relations and partnerships with academic researchers. Hence this is the community our small team can support during this initial release. We are working on a broader
release under a more permisive license with the goal of an open source release of Dryad, in collaboration with the MSR-SV team.