DB2 database -> does it continue to be platform-specific? (iSeries, LUW, z/OS)
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.