As menitioned above, partitioned tablespaces in DB2 for z/OS is called range partitioning. This feature will be available in DB2 for LUW version 9.1 later this year (beta is available now). Range partitioning is primarily used for administrative ease of large tables, such as where one partition can be down for a load, while the other partitions can be on-line. You can also archive one partition at a time with a partition backup.
DB2 for LUW supports hash partitioning where each partition is on a seperate node (logical or physical) primarily for the purposes of parallel processing of a singe long-running SQL statement. The more different physical nodes there are, the more linear scalability one can achieve with the parallelism.
There are some exceptions to the above, such as the fact that parallel processing can be done on range partitioned tables, but the above is primary difference between the two.