The reason I use the term "aggressive' is because of the way it behaves when there are also native ASIO drivers on the system. it will assert itself as the primary driver in most cases regardless of how you set the system up as long as you have not disabled it.
What I mean by that is that if both ASIO4ALL and a soundcard's native ASIO drivers are both enabled in sonar, but you have the native ASIO drivers being used and "at the top" - then close the system, ASIO4ALL will now be your output the next time you open sonar.
I can't say this happens on ALL systems. but I have experienced it myself and I have talked to a lot of folks in the SHS and MC forums which have experienced this as well.
I suspect (but have not tested) that it might behave that way in the windows environment as well. have you see any behavior like that in your windows setup?
NOTE: ASIO4ALL does not use the ASIO drivers of the soundcard with native ASIO drivers. ASIO4ALL is a WDM wrapper. so if you're using ASIO4ALL to run your soundcard which has native ASIO drivers, you're not using that soundcard in ASIO driver mode, you're using it in WDM driver mode but fooling the host into thinking you're using ASIO drivers.