this is an interesting article
http://www.google.be/url?sa=t&source...x51s7ZoVP3NJ1g
the summary in also in english. (page7)
the main conclustion is that bigger vehicles like suv's are a danger to smaller cars because they're heavier and as a result require that their impact structures are stiffer to compensate for this greater mass in a colission with a static and solid obstacle. also their heiger stance causes their impact structures not to interface with those of smaller vehicles. coupled to their greater stiffness they're more likely to cause damage to lighter cars.
it's recomended that these kind of tests become part of the standard crash test.
edit: it's interesting to note somewhere in the article it's mentioned that all vehicles off all types and weight classes are generally equally safe in a colission with a solid object, something that froms the basis of the crashtest.
this would lead me to conclude that if colissions with various vehicles of different weights and sizes where part of this test too, vehicles would become more safe in this respect too, especially since carmakers generally cover a whole range of vehicles and could make sure their entire range was "crash compatibel"