Apple clearly needs to get on the ball with web browsers. Their "offcial" web browser, IE, is lagging. Microsoft is not giving it any priority, and the Mac platform is suffering as a result. Look at all the bad press OS X got (and still gets) with regard to web browsing. Even people who switch from PCs to Macs will still tell you they find web surfing on the Mac a sub par experience to Windows, mostly due to speed.
Apple could go the route of developing their own browser, but that would really drive a wedge between Microsoft and themselves, one which they don't really need now that there is no 5 year agreement for MS to continue to develop Office.
Instead, Apple has an alternative option.
It can hire developers and contribute to the Chimera project, and it can do it completely under the radar screen. With Chimera being open sourced, Apple can contract developers to work on it, all without officially endorsing it or snubbing MS. When Chimera finally reaches completed status, Apple can include it in the OS X installation alongside IE, but not selected as the default browser, much like Navigator was inlcuded in OS 8.6-9, but not installed by default.
Apple really needs to keep it's options open. Everybody worries about what would happen if MS killed Office for the Mac, but what's more likely is that MS ceases development of IE for the Mac first. MS derives no money from IE for the Mac, and it takes up enourmous resources. Apple needs to be prepared for the inevitable and keep the other players healthy and ready to pick up the slack of IE.