DB2 database -> does it continue to be platform-specific? (iSeries, LUW, z/OS) Wikipedia says DB2 is no longer Platform-specific:


  Historically and unlike other database vendors, IBM produced a platform-specific DB2 product for each of its major operating systems. However, in the 1990s IBM changed track and produced a DB2 "common server" product, designed with a common code base to run on different platforms.


If this is the case, why are there different drivers to connect to DB2 for iSeries and DB2 for Linux, UNIX and Windows? (I'm not sure if DB2 for z/OS has its own driver as well.)
I don't think your assumption about "different drivers to connect to DB2 for iSeries and DB2 for Linux, UNIX and Windows" is correct. There is a single IBM Data Server Client that is used to connect to DB2 for LUW, DB2 for System i, DB2 for z/OS, and Informix servers. 

However, what you quote seems to reference DB2 server software, not drivers, and there are still different versions of DB2 servers for LUW, System i, and z/OS. They used to have quite different SQL dialects, but these differences are being reduced.