There is a move among development teams that support agile to assume that developers should be interchangeable. The Agile Manifesto specifically states that the individual is more important than the process.
Partly this is a misinterpretation of lean – where team members are members without titles. This should not mean everyone is the same – just that everyone is equal.
The reason – ownership is “obviously” bad. This is true if ownership means exclusivity – to the exclusion of knowledge sharing. Instead, think of ownership as vision holding. Business representatives own the system concepts, project managers own the process to completion, team leads own the processes they need to meet their goals and developers own code.
By all means use pairing and agile techniques to make sure the knowledge is spread, but allow a developer or a group of developers to own what they create. Allow them to be proud of their work and keep it running smoothly. Allow the developers to be motivated by making them more than just a part of the solution. We are craftsmen, respect our gift.