AJ, a blowout in the rear is more dangerous because it's more probable that fishtailing will occur. I've had a front tire blow out at over 200 km/h, and while it was a very noisy event, (running on the rim with the tire spinning on the rim and getting shredded) I didn't get close to losing control. I've had a rear tire grenade on my Buick wagon going 60 or so and it wasn't much fun and could have easily ended badly. I also had a rear tire lose all pressure in my A4 quattro, and if it hadn't been for the atrocious rumbling, I wouldn't have noticed it as long as the tire didn't fall off! (I believe all quattros should have a tire pressure monitoring system because of this).
My '89 Scirocco's manual said to always put the tires with more tread on the front (in case of a FWD car). Back then the recommendation was to put the tires that had more tread left on the powered axle.
Quote from my '96 Audi quattro manual:
Quote:
If the front tires are more worn than the rear tires, then you must rotate the front tires with the rear tires as shown in the illustration. By doing this, all tires will have approximately the same service life
Audi says this because the tire circumference on a quattro must be within 3% of all other tires to prevent excessive wear in the Torsen differential. I don't think that 3% more or less tread make a big difference in traction, unless the tires are nearing their end of life, so I don't think the whole issue applies to a quattro or other AWD car (as long as the tires are all reasonably new).
I asked my German dealer last year about the tread issue. He said opinions were split, but the newer recommendation was to mount the tires with more tread on the rear. Th dealership does that, and it is in line with what the TÜV and DEKRA recommend.
Michelin in Germany elaborated by saying that the predictability by how the car will behave is not changed when tires with more tread are mounted in the rear. Contrary to that, loss of control in the rear with increased traction due to considerably more tread on the front wheels leads to unpredictable and probably unrecoverable behavior of the car. They also said that more tread on the rear tires means that the car will remain more stable ("track better") when braking in curves.