Well, they share one app (iTunes). I was more thinking iPod classic (I group iPod touch in with the iPhones), but I get your meaning. Yes, the risk is that they don't jump where you want them to go, but that is the same risk as you doing nothing. The users are going to jump.

Microsoft should have been fine, but it looks like they are so locked on what they are doing now and allowing middle managers to play politics instead of technology (see the Clear Type stories for instance) that they are heading to the iceberg. The Titanic was "unsinkable" until it hit the iceberg. Microsoft's software is not really geared for mobile and replacements with reputations are appearing on other platforms. I believe Microsoft's strengths now are inertia, document formats, and servers (specifically Exchange and SQL).

If I was in charge of Microsoft, I would probably do a modified version of the OS X -> iOS strategy. Use a beefed up version of Silverlight refocused on touch and make sure the new apps run under Windows 7 also. Make sure you ship an "App Store" to enterprise customers that automatically installs the right apps on machines and does backups.