From my viewpoint, IBM is not depending on Apple for anything beyond first-row testing and establishing a developer base for them. They're being smart here, making a chip that would enable them to better compete against the newly found scalable solutions such as those from Dell. By being a seperate technology, PowerPC rather than Xeon, IBM can create a "developer gap" to retain customers. In this case, Apple is the one doing the majority work for IBM to encourage this gap with a user-friendly home machine.
Quite brilliant if you ask me.
