This overview of the Commercial Crew Program on NASA's site describes the difference between Commercial Crew and previous systems (I have numbered the original bullet points for easier reference):
How NASA’s Commercial Crew Program is Different
(1) NASA's Prior Approach for Obtaining Crew Transportation Systems:
(1.1) NASA devised requirements for a crew transportation system that would carry astronauts into orbit, then the agency's engineers and specialists oversaw every development aspect of the spacecraft, its support systems and operations plans.
(1.2) An aerospace contractor was hired to build the crew transportation system to the design criteria and the standards NASA furnished.
(1.3) NASA personnel were deeply involved in the processing, testing, launching and operation of the crew transportation system to ensure safety and reliability. The space agency owned the spacecraft and its operating infrastructure.
(1.4) Every spacecraft built for humans, from Mercury to Gemini and Apollo to the space shuttle and American section of the International Space Station, was built and operated using this model.
(2) Commercial Crew's Approach for Obtaining Crew Transportation Systems:
- (2.1) NASA's engineers and aerospace specialists work closely with companies to develop crew transportation systems that can safely, reliably and cost-effectively carry humans to low-Earth orbit, including the International Space Station, and return safely to Earth.
- (2.2) Interested companies are free to design the transportation system they think is best. For the contracts phase of development and certification, each company must meet NASA’s pre-determined set of requirements.
- (2.3) The companies are encouraged to apply their most efficient and effective manufacturing and business operating techniques throughout the process.
- (2.4) The companies own and operate their own spacecraft and infrastructure.
- (2.5) The partnership approach allows NASA engineers insight into a company’s development process while the agency’s technical expertise and resources are accessible to a company.
According to 1.1 and 1.2, for past programs, NASA came up with a set of requirements and hired a contractor to build a system meeting those requirements. Meanwhile, 2.2 seems to say that NASA awards contracts to companies with proposals that meet their requirements for Commercial Crew. However, these processes don't sound so different, and apparently past programs involved proposals from different companies too; for example, the Wikipedia article Space Shuttle design process states that "Lockheed Aircraft, McDonnell Douglas, Grumman, and North American Rockwell submitted proposals to build the shuttle" (citing The Space Shuttle Decision). So how does the development of Commercial Crew systems for NASA differ from how things were done in the past?
A more significant difference seems to be described in 1.3 ("The space agency owned the spacecraft and its operating infrastructure") and 2.4 ("The companies own and operate their own spacecraft and infrastructure"). But what does that difference in ownership mean in practice?
What other differences are there between Commercial Crew and previous NASA programs?