ActiveSync Ver.4以降にWiFiによる同期が外された理由：Windows Mobile Team Blog

Conspiracy theories abound. Because WiFi to an Exchange server still works, some people have suggested we did this to sell more Exchange servers. That’s definitely not the case. Exchange has considerably more customers than Windows Mobile (although we’re growing quickly!). Hurting Windows Mobile to make Exchange do better just wouldn’t make any sense. Don’t get me wrong, I’m sure that the integration between Exchange and Windows Mobile has driven sales of both. But we’re not about to hurt one product to help the other. If nothing else, Windows Mobile and Exchange are in different divisions, and both are expected to make money on their own. So even if Exchange came to us and said, “Why don’t you hurt yourself to help us?” we’d say “No thank you.” (Okay, our response would be less polite than that….)

Windows Mobile Team Blog にActiveSync Ver4以降にWiFiでのActiveSyncの同期が外された理由の記事が掲載されています！
シリアルケーブル、USBケーブルはPCと直接繋ぐのでセキュリティの問題も殆どない、Bluetoothは一応暗号化できるのでとりあえずサポート、WiFiは暗号化も設定すれば可能だけれどもWiFiというよりはEthernet上での同期を外したということらしいですね？　別にExchange Serverを売るがために外したということでは無いようです(^^;
今後はどうか解りませんが、WiFiによる同期はすばやく出来るのでActiveSync自体に暗号化を盛り込んでいただきたいものです。
http://blogs.msdn.com/windowsmobile/archive/2006/11/08/wifi-did-you-do-that.aspx