Most businesses (in number, in dollar volume, and in employment) in the U.S. are small businesses. If they have a firewall at all, it's just a little NAT router. Since Microsoft's stuff is browser based and requested from the inside, such a firewall is no protection whatever. We're not talking hackers here, were talking about a vendor who's software agents are within the firewall.
Most businesses in the U.S. do not have any IT staff whatever. They generally have one person who knows just enough about Windows to screw it up. Most are getting concerned about the cost of Microsoft's software, but have no intention of going elsewhere.
I personally am all the IT staff about 220 such businesses have (about 150 are active (call for my services at least once) in any year). Because I'm "expensive", they don't have me do more than the minimum to keep their systems running.
My larger clients (those with over 20 workstations) are little better off than the smaller ones.
Very few of my clients even have anyone on staff who understands what a directory is. When asked where they keep their document files, they say "in Word" and are totally mystified that I don't consider this sufficient information. This is typical of most businesses in the U.S.. They have no defense whatever against anything Microsoft wants to do.