Well, not really, Tyll.
I was using the word "control" in the same context as Dreadhead did. You can very much choose order which results in non-linearities without really caring what the resulting curve is, when building a passive crossover. You might not like what you have to do in terms of driver choice, or time alignment, but it's doable (btw, driver choice is perhaps even more critical in a DSP scenario, that's why the people that Dreadhead mentioned above contact out their driver design).
In a DSP scenario, like Dreadhead mentioned, this is harder. You have to actually control the curve itself in order to deal with the non linearities that the system itself inserts into the chain.