you're exactly right, Xcel has a program where they give owners money to implement energy-saving elements such as increased insulation, high efficiency HVAC systems, solar panels etc. because it saves them money since they don't have to build out as much energy production infrastructure.
As architects working with our sustainability consultants, we analayze numerous enery savings options and pick which is the best for energy efficiency and our project.  It's a total free-market incentive.

Personally, I find this initiative insulting because it implies architects and sustainability consultants are wrong in choosing other options over green roofs.