I'll agree it is confusing. The article uses "SSDT" to refer to the whole product, including the SSIS development tools, however what they really mean when they say "target" is that the DB Admin tools (from SSMS) and Data Dude functionality (from Visual Studio 2010 Premium/Ultimate) that was folded into SSDT can target all those platforms. The SSIS development portion of SSDT can only target SSIS for SQL Server 2012. To manage SQL 2008 packages you will still need BIDS 2008, and for SSIS 2005 development you'll still require BIDS 2005.
There are no special teachers of virtue, because virtue is taught by the whole community. --Plato