Layered on top of these various product development practices, we often hear about the concept of "Lean Startup," which was pioneered by Mary Poppendiecks, Tom Poppendiecks, Eric Reis, Ash Maurya, Marty Cagan, Jeff Patton and many others. Speaking broadly, while Agile methods focus on the "how, when, who and where" of rapidly iterating through features and eliminating waste, Lean methodologies focus much more on product validation; the "what" and "why" of these new features we're building and whether they will be successful.
This is a good question. First, one lifecycle clearly does not fit all. Teams find themselves in a unique situation: team members are unique individuals with their own skills and preferences for working, let alone the scaling/tailoring factors such as team size, geographic distribution, domain complexity, organizational culture, and so on which vary by team. Because teams find themselves in a wide variety of situations shouldn’t a framework such as DA support several lifecycles? Furthermore, just from the raging debates on various agile discussion forums, in agile user groups, at agile conferences, and even within organizations themselves it’s very easy to empirically observe that agile teams are in fact following different types of lifecycles.