[snorlax]

Wouldn't it just be easier to just use Golf chassis to make the sportwagens instead of continuing to use the mk5 chassis?

All '09+ Sportwagens are on the Golf chassis. There aren't that many differences underneath a MK V and MK VI Golf. I've had both in the air next to each other, and most parts were interchangeable.

If the wagons and sedans are made in Mexico, why wouldn't they both be on the same platform? They could just change the name of the Golf Variant to sportwagen or Jetta wagon.

The unibodies are completely different, the wheelbase, width and length are all greater on the '11 Jetta. The current wagon body just won't "slip on".

It is a cost savings move to keep the current JSW in the line right now rather than engineer an entirely new rear end for the new car. In other markets VW offers the Golf Plus, Passat wagon and the all-new Touran for those that need more room than the current Golf Varient/JSW.