I just ran through the same steps you did and cannot figure out why it is detecting that the platform is not compatible. If I double click the cmd file I use to install version 4 of the Widi connection software, it installs just fine. It really doesn't seem to like being installed remotely. I'm guessing it has something to do with the temporary profiles that remote installers create. For instance c:\users\AIF1F7~1~D20\AppData\Local\Temp. I don't see anyway to tell msiexec what temp folder to use so I'm also stuck. I'm going to try one other thing which has worked for me in the past. I'm going to script an autologon with a runonce command to see if it will install with a "real" user profile. This adds some time to the install and reboots are never fun since you have to schedule them with users, but perhaps it will work.
The requirement about factory preinstalled is nonsence. The real requirement is that you have an Intel graphics adapter to go with your Intel WiDi/WiFi card. The trick is to get the full Wireless Proset software/driver and not just the drivers. There are two files on their site, one labeled Ds.exe and one just labeled s.exe. Get the larger file that around 80MB and do a default install of that. If you don't have shortcuts in your start menu afterwards, you have the wrong file.