Can we create DTS Package in DTS package in SQL Server 2005 or higher version?

http://social.msdn.microsoft.com/Forums/en/sqlgetstarted/thread/e4729205-87cf-4816-8dea-5c5289c592af

the functionality of SSIS is similar to DTS. but SSIS Package is not a DTS Package.
As if it will be same as of SSIS then why we need to migrate DTS Package to SSIS in 2005. Some times it can be achieved with tool (Migration) but for some cases we need to manually change the DTS Package to run it as SSIS.