One idea is that class ownership is an organizational mechanism for use with a team of lesser experienced developers.
The assertion is that a team of highly skilled individuals tend to be highly collaborative and will develop a good understanding of their problem space. Consequently, each has the ability and understanding to alter, re-factor or modify classes within their problem space as required. Whereas a team of lesser skilled developers can make use of class ownership to help manage their development.
Is there a pattern here of diminishing returns for class ownership as development teams become more skilled?