First of all, the Bionic has ~3.5GB of app memory, so the need to move apps to SD should be non-existent.
For the other issues/confusion, here's how the directories shake out:
/mnt/sdcard -- this is actually the INTERNAL memory, and is ~8GB. It is separate from the storage space used for OS/apps/etc. Why they name it "sdcard" is beyond me, but I have my thoughts*
/mnt/sd-ext -- this is your removable SD card
*If I had to guess, the "internal" storage is mounted as /mnt/sdcard because that way it will function correctly even if there is no external SD card inserted. Most applications are written in a manner such that they will search for /mnt/sdcard for data storage functions, and so forth. This way, apps don't have to be re-coded in order to correctly access the internal storage as designed. Obviously, the best thing to do would be to code apps such that the user can specify the directory to save files, but until recently, few devices had both large amounts of internal storage and SD card slots. I have a Galaxy tab (w/ no SD card support), and the 16GB of internal storage is also mounted to /mnt/sdcard on the file directory. I thought it was strange at first, but then realized some apps probably won't function correctly if that directory doesn't exist. Again, just my best guess.
A better way to do it would be if file paths in apps could be coded with environment variables, such as in Windows, i.e. "%sdcard%". Maybe this functionality does exist??? I don't know. That way, the device could define the variable and assign the correct path for external storage, rather than having the path hard coded into the app.
http://www.androidcentral.com/droid-bionic-has-16gb-internal-storage-you-cant-have-it-all