Hello Wafn,
Sorry if I didn't explain this completely. Let me rephrase a bit. You most certainly CAN play music on SYNC from a USB flash drive. You cannot, however, play PROTECTED content from these USB flash drive devices. You can think of protected content as a locked file that requires a key to be played from a device. Your computer and the devices I mentioned above can use these "keys", while simple devices like USB Flash Drives cannot (they can only store the locked file).
Now, let's talk about how protected content is obtained. If you download songs online from sources like Wal-Mart, MSN Music, iTunes, Zune Marketplace, and so on, that content comes protected. Normally when you rip CDs to you computer, that content comes unprotected. There is a setting in Windows Media Player that determines whether the music you rip from CDs will be protected or not. By default it's unchecked but you should have a look to see if it is for you or not. You'll be looking in the "Options" menu. Here's a screenshot of what it looks like:
If it's unchecked, you should be able to rip music from CDs, copy that music to your USB flash drive, and enjoy your favorite tunes in your new Ford Edge.
I hope you found this information helpful.