Yes, some BMW salespeople can be jerks. But from the point of view of the dealership, it makes sense to offer test drives only to those who have deposits (or have the deposit in hand), especially if the dealer has only one or two demos and is expecting very limited alotment for the coming weeks.

Regarding the Tischer BMW case, it's totally understandable that the guy was turned down for a test drive. 19-year-old with an E46 in for servicing wandering around a metropolitan area dealership (~8 miles from DC). Doesn't sound like a serious customer at all. At the very least, he should have made an appointment ahead of time. This tells the salesperson he is at least somewhat serious. Dealers in rural areas may be more hard pressed for sales traffic, so are likely more willing to give test drives. The behavior of the general manager is pretty inexcusable, though.
I hear that Lexus dealers and service reps are very nice and accomodating.