Actually not AMD and Motorola, but AMD and IBM. It's no coincidence that the AMD Opteron and the IBM PPC970 have similar thermal and performance characteristics.
This is coincidence, the 970 and K8 had been in development since way before AMD and IBM joined forces. IBM had a marginal impact on the K8 design only when it came to optimizing its SOI circuits, a field in which IBM had much more experience than AMD. Consider that AMD's current process and the future 90nm SOI process has been designed together with Motorola, not IBM. Their 65nm process will be jointly developed with IBM. Also the next processors which will come out from them will probably have much more in common since now both their development teams are working side by side at the IBM East Fishkill facility.
