They're the same except the toolkits are different and the T2 had a slightly less reliable motor whereas the original DC19 with the clear handle was a proper cylinder vacuum.
The tools differ, the T2 uses click fit, same style as the DC25, DC33, Dyson balls, DC39, etc. The DC19 uses DC08 style fitting tools.
The DC19 has a nice sturdy metal wand and a decent hose, the T2 has a plastic wand and the connections always got loose and leaked air whereas the standard DC19 never had this issue. Also the T2 has a slightly shorter hose. One benefit of the T2 is that you can have just the hose cuff fo easy car vacuuming without the handle, but then again that's why I prefer the DC20 to any DC19.
The DC19 also has on board tool storage on the back of the vacuum, the T2 has a bulky tool holder on the wand that clips on
Floortools differ as well, standard DC19s came with the flatout head and the T2 came with the typical Dyson designed DC05 style of head