I read somewhere that the latest G2 (with USB controller) has some planes that did not come with older versions of G2. My understanding is that some of the downloadable airplanes from the G2 website don't work unless you have the newer version with the added planes as a base. A quick look at their website didn't reveal any information about this .

What, if anything, is missing, and is it available anywhere (for no cost) for registered users?

go to Tower hobbies they list the planes in the "tech" area for each one

So, the new additions are the Huey heli, and Ryan and Electro Streak planes. Next question is are they available for registered users?

If I'm not mistaken, all of them should work with G2, be it usb or the old gameport connection.

To answer your question, If you have the plane on either the sim disk, or one of the add-ons, you can download them and use them. i.e.... You cannot download the Harrier and use it unless you have add-on disk 4

I understand that, but the point is that if you bought Realflight G2 with the USB controller, you got three planes that you didn't get if you bought G2 with the gameport controller. So any downloaded planes based on those three new planes can never be used by those who don't have the USB version of G2.

Correct!

Right .. to use the electrostreak, ryan, or huey with the "non-USB" version of G2 you need to purchase Add-on 4. You can not download them for free even if you are registered.

FWIW I have add-on 4 with the older version of G2 and it is great.

Carl