A solution
The missing loops do belong in GarageBand '11, and have to be downloaded from Apple and installed into GB. The problem is, GB is broken in this respect, and it will not download the loops, and the App Store will also not update the loops. GarageBand will say it is downloading them in Software Update, but it will not do so.
I called AppleCare about this, and it took a couple tries, but we got it solved. It's complicated to do so.
It is, the support person said, the one thing broken in GB '11. Anyway, here's the procedure that worked to get them to install. (Hope I'm not giving up any state secrets here; they didn't swear me to secrecy and others do have the problem.)
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First thing to do is go to GarageBand and make it go through its fakeout cycle telling you it's updating the loops. Click on any gray loop's download arrow, and tell it to download it now. It'll open App Store, and that won't download anything, and it'll all fail. Quit App Store and GarageBand.
Next, you need an administrator login user. I created one, called "apple" -- do this in the Users & Groups panel in System Preferences. (You do need admin privileges to do this; you may already have them in your own login, and thus not need to create an administrator login.) Gave it an easy password. Then, with Fast User Switching, I logged in as the administrator "apple."
It'll take a few minutes for your machine to set up this new user, so be patient until it's all logged in. (The mouse will be slow. You can change that in System Preferences Mouse panel if you want to.)
Now, open a Terminal window. Fastest way to do this: Spotlight (Cmd-Space), type in "terminal" and hit Return key once Terminal is highlighted in the Spotlight list.
Let Terminal get all set up, with a cursor available.
You'll see something very like:
Last login: Sat Jun 29 18:55:22 on console
ComputerName:~ apple$
At the cursor prompt, type:
sudo softwareupdate --list
Hit Return. Now you'll see:
WARNING: Improper use of the sudo command could lead to data loss
or the deletion of important system files. Please double-check your
typing when using sudo. Type "man sudo" for more information.
To proceed, enter your password, or type Ctrl-C to abort.
Password:
Type in the password you created, and hit Return. Now you should see:
Software Update Tool
Copyright 2002-2010 Apple
Software Update found the following new or updated software:
* GBExtraContent-1.0
GarageBand Instruments and Apple Loops (1.0), 1170290K [recommended]
Select and then copy (cmd-C) the GBExtraContent-1.0
Now, type at the ComputerName:~ apple$ prompt:
sudo softwareupdate --install GBExtraContent-1.0
Now, you'll see the update take place. It'll look like this:
Software Update Tool
Copyright 2002-2010 Apple
Downloading GarageBand Instruments and Apple Loops
104 KB of 1.2 GB
1 MB of 1.2 GB About 14 minutes
2.5 MB of 1.2 GB About 10 minutes
4.1 MB of 1.2 GB About 8 minutes
6.1 MB of 1.2 GB About 7 minutes
[This will continue until it's all downloaded.]
What you're seeing in that counting of GB and minutes is the countdown of the download and the install time. Let it run until it completes.
Give it a couple minutes to complete installing, and then start GarageBand in the admin login. It will take some time for GB to start up, because it's the first startup for this user. Several minutes.
Once it has completed (it takes a while, as I said), go to the Loop Browser. They should all be there, no gray.
Quit GB and go to your normal User and start GB there. The loops should all be present. If not, quit it and restart it. Now they should all be there.
At least, this worked for me this way.
