If you haven't noticed already the Nexus 7 isn't actually using the tablet version of Android Jellybean. It's using a hybrid version between the phone and the tablet to make use of the 7-inch screen while keeping text big enough to read.
Now if you really want to make your Nexus 7 have the proper Android tablet UI, you can use this neat little hack.
Note: Your device will need to be rooted for this! You can check this out if you want to root your Nexus 7 - Root Nexus 7
Enable Full Tablet UI on Nexus 7
1. Download a file explorer which allows you to explore the root files in your device. File Expert is a good one.
2. Go to "/system" using the file explorer. In that folder should be a file named "build.prop.". Make a copy of that file anywhere just as a backup.
3. Then open "build.prop". Look for the property "ro.sf.lcd_density". The number you should find is 213, change it to 170 or lower.
4. Lastly reboot your Nexus 7 and you will now have the full tablet UI experience!
If you would like to restore just change the number back to 213.