I love these threads... Everyone has 'heard from so and so' about all kinds of differences...
They're the same car. Different markets get different options and equipment. If it weren't for the fact that the Jetta is VW's biggest seller in North America, we'd all be driving cars with 'Vento' on the trunklid. Nothing else would be different... We'd still have the bigger bumpers and and all the other stufff.
The fact is that the Jetta (or Vento) didn't sell well outside of North America. The name change was an attempt to change the car's image to boost sales. Same reason the MkIV's are Bora's.
Here's my own addition to the 'I heard from so and so' fun: Volkswagen will no longer be selling the Jetta (or whatever you'd like to call it) outside of North America after the MkIV's production run is over.