Sorry forgot to include this information I got from an IBM Db2 V8 help page
Specify separate table spaces for indexes
Indexes can be stored in a different table space from the table data. This can allow for more efficient use of disk storage by reducing the movement of read/write heads during index access. You can also create index table spaces on faster physical devices. In addition, you can assign the index table space to a different buffer pool, which might keep the index pages in the buffer longer because they do not compete with table data pages.
When you do not place indexes in separate table spaces, both data and index pages use the same extent size and prefetch quantity. If you use a different table space for indexes, you can select different values for all the characteristics of a table space. Because indexes are usually smaller than tables and are spread over fewer containers, indexes often have smaller extent sizes, such as 8 and 16 pages. The SQL optimizer considers the speed of the device for a table space when it chooses an access plan.
I guess what Sathyaram is saying is that you can only specify an index tablespace for all indexes (indices?) built on a certain table at the time when you create the table, and you cannot change it afterwards without re-creating the table.