Oops, after a quick check it turns out it's the "add on packs" that are free, the "expansion packs" are still being sold - I can never keep those two straight. Here's the link for the free downloads so you can see what's in them - http://www.realflight.com/free-g4-add-ons.html

Well, you wouldn't be starved for choices of airfield or plane/copter without the expansions/add ons but they do contain some of the more interesting ones. Also a lot of the user created planes and variants require one or more of the expansion/add on packs.