Even government organizations are buying lots of iPhones, even though Apple is an obnoxious vendor for those organizations to deal with.
Microsoft sells stuff these days by bundling product licensing. So unless Apple does something really dumb, you're not going to see enterprises mandating anything Microsoft mobile other than ActiveSync anytime soon.
It was easier for things like this to happen back when everyone was carrying a company-issue blackberry (because blackberries were too expensive for most consumers.)
These days, companies are increasingly just letting their employees connect personal devices onto their exchange servers (with policy management) and enjoying the savings from not having to pay for the device, data, or both. I can't see either group (companies and employees) being happy about reversing this trend.
The only reason not to is a DoJ monopoly investigation - and Apple would have a task persuading the government that they are the victims of monopolies in the smartphone world!