Russell: you are correct "Sort of".
The modern Tig units have a lot more adjustability and are capable of better quality welds on a larger range of compositions than earlier simpler welders.
A simple set up that is pretty much Al. capable is a Miller Dial arc (an ac/dc machine) with either an aftermarket high frequency box or better one of the dial arc models with the HF built in.
The HF feature allows non contact starts and eliminates contaminating the tungsten which results in poor quality welds. Using the ac as the source breaks up the oxides.
Not as nice as a full featured inverter unit but then at 10 to 25% of the price it is a good way to start.

Welding Aluminium is just another process once you learn the do's and don't's it boils down to selecting the correct filler rod and parent metal cleanliness plus enough practice to become good enough to do what you need to do.
The other thing about tig is that it is very sensitive to external contamination if the shielding gas fails to keep the weld covered until it has cooled below the critical temperature.
This means that tig is normally an indoor process to ensure good draft control.

Any way you want to look at it Tig is the most expensive common process for welding but there are situations where there is simply no other practical choice. Thin A. as in Steves application is one of them.
I personaly have avoided entering the tig owners club as the amount of welding that I need tig for is minimal.
I can go to a fellow that has a set up that I can use(fun) for non critical stuff or get him to do for critical welds ($$$). I would never get enough practice to be capable of the critical welds to my satisfaction.
Just as at my age my eye sight is not good enough nor am I steady enough to sit all day hand soldering surface mount components with lead free solder to build up a prototype or concept design. Thank god for relatively inexpensive fairly quick prototype houses.:)
Terry