I completely agree. Heterogenous networks are the way to go, but Microsoft will not allow that to happen if they have any choice. Their strategey has always been end-to-end ownership of the network - from handhelds all the way to the enterprise-grade servers (although, I don't believe that Microsoft
really understands what it means to be enterprise-grade the way, say, Sun does).
The huge problem with heterogenous networks is managing them. I work in an environment that uses Sun, HP, AS/400, Winnt, and Linux to name a few (sorry, no Macs

). Around each of these platforms has grown different empires; the NT guys, the Unix guys, the mainframe guys, etc. Getting each group to agree with the others on
anything is usually a lengthy and painful process. And Microsoft knows this. It's exactly this sort of culture that they sell to avoid - "Wouldn't it be so much easier if there were only one platform to manage (Windows)?" They're partially right, damn them, but it would do nothing for the ultimate security of the network...