That is inconvenient... When I'm at work, I connect my MacBook to internet via ethernet and don't use wifi on my iPhone 4. So now when I want to quickly throw a few songs on my iPhone before I leave, instead of just going over the USB cable that is connected, it uses 3G to download them from the cloud... What the heck! That seems crazy to me. I would think the iPhone would recognize that the songs I'm adding are both in the Cloud and on my MacBook locally and use the fastest route to get them on iPhone, which would be USB over 3G. I don't understand why'd they'd do away with syncing over USB entirely... arg.
This might not be the recommended approach and I don't know if it will cause problems down the road, but you can have it both ways. Just not at the same time.
When you want to sync via USB, go to your iPhone Settings --> Music and turn off iTunes Match. Then plug the USB cable in.
After you disconnect, turn iTunes Match back on. Disgregard the warning about all your music libary being replaced - it's a little (or wildly) misleading. It's not replacing your music files, it's replacing the list of music files that the Music app displays (though there are complaints on this board that it does wipe out the music, that hasn't been the case for me).
You should now see that the songs you just synced via USB do not have the "cloud" icons next to them.
For good measure, force your Music app to quit by double-tapping the home button, then holding your finger on the Music icon until it squiggles and tap the "x". Not strictly necessary, but I've found that the Music app doesn't always recognize when you yank it around like this, so it may temporarily show the wrong list of music if you don't quit it.