Manufacturers these days (including BMW) design and build their cars to meet a set of internal and external (EuroNCAP for example) crash worthiness standards and guidelines. Usually a set of tests based on predetermined parameters and boundaries.
Because of that, it it very difficult to assess how a particular car will do in a different kind of situation (test or real life) with different variables (speed, location of impact, object impacted into, etc.) outside the scope of those with which it was built in mind for. The S Class that was totaled is a pretty good example. Judging by the state of it, it was most probably involved in a very high speed accident with huge forces at work, crashing into all sorts of things. Put any other car into the same situation and it would most probably end up the same way.
That's why it wouldn't be surprising to see a particular car (any car) perform below expectation when subjected to a new kind of test, such as this one. BMW probably didn't design their cars to meet this specific test. Hardly surprising given it would be impossible to design and build a car that can deal with every situation thrown at it.
Especially since this crash test is a particularly tricky one because it attempts to simulate a bigger, taller SUV or truck crashing into the cars (which are medium sized luxury sedans), a so called crash compatibility problem. They don't normally do tests between cars of different classes. All the usual crash test ratings given are relative to their own vehicle classes.
That said, to ignore the results of this test entirely would be a folly as well because it clearly shows a weakness. Although obviously one result of a particular crash test shouldn't be use to conclude the overall crash worthiness of any car.
