[nailer]

If Apple could have developed their own proprietary rendering engine they would have. Jumping on KHTML meant they could get a working, OS X UI compliant browser when IE for OS X was no longer being maintained, even if the guts of that app had to be shared with others.

[rsynnott]

While that's true for the LGPL components of WebKit, they were under no obligation to open source the BSD components, which they largely wrote.