Partitioned tablespace? I think you are confusing DB2 for z/OS (mainframe) with DB2 for LUW. They are very different at the physical level. Only DB2 for z/OS has partitioned tablespaces.
With DB2 for z/OS there are several very good reasons for having separate tablespaces for each table. I don't want to get into that discussion here since you apparently have DB2 for LUW (you mentioned DMS).
With DB2 for LUW, tables are reorged, not tablespaces. If you are going to recover just one table, then you can recover the tablespace if it has only one table, but not many people recover just one table.
From a performance point of view, a lot depends on your disk subsystem. If you have multiple containers spread among multiple disks (or multiple arrays) then it does not make much difference. If you have just one or a few containers, then you may want multiple tablespaces to spread the data around.
When IBM runs TPC-H decision support benchmarks for DB2 (see www.tpc.org) they have multiple tables in each tablespace. Each tablespace has many containers spread across the disk arrays. Proper matching of extents, prefetch size, and number of containers is important for decision support systems, much more so than the number of tablespaces.
M. A. Feldman
IBM Certified DBA on DB2 for Linux, UNIX, and Windows
IBM Certified DBA on DB2 for z/OS and OS/390