hi mmbg,
i think the bring-your-own-device model suggests otherwise. or put another way, i think the mobile market suggests otherwise. or put another way, folks actually use several sorts of device to attach to a network.
it is rare for folks to employ non-ms personal computing devices within an enterprise (because windows is still pc-dominant) and about equally as rare for folks to use windows mobile devices to do things like accessing their email (because android and apple dominate mobile).
if an enterprise wants to have a single trust data security model, then a multi-os service makes decent sense.
that's one part of the argument.
another is that folks like credit card companies and banks that deal with money also don't necessarily want powerful software providers inside their kimono. so again, a new player makes sense.
another is that hard drive people like seagate and chip people like intel don't always have common interests and in the case of seds, wave can help the hard drive companies avoid being dependent on chipzilla.
so far, however, the argument hasn't taken in a way that delivers revenue.