Your inference that DB2 was only available on AIX is incorrect. DB2 in also on all UNIXs and LINUX.

"The key WPAR program that IBM is adding into the Enterprise Edition release is called Workload Partition Manager, which was previously an add-on product, and this is what allows AIX WPARs and their workloads to be teleported from one physical machine to another using what IBM calls Live Partition Mobility."

Live Partition Mobility - Introduced with Power6 systems and migrates the entire partition including the OS. It is initiated and managed by the HMC (Hardware Management Console)

Live application mobility - migrates a WPAR to another machine or LPAR, feature of AIX 6 (and can thus be done even on Power4 or Power5 systems)

And Mainframe, also Windows and iSeries as well IIRC.