The most specific discussion of "why bmw antifreeze?" I've seen was an article in Roundel about 6-7 years ago. I can't find a link to it, but here is a thread in the E46 forum summarizing it [with the comments making the normal arguments why its the same as Zerex GO-5 .....]:
The "why BMW only" coolant question answered - E46Fanatics
Since mine has the fluid/thermostat/etc. changed about 20k miles before I bought it, not something I have to think about for awhile ....