They make money selling 'premium' toys. Aircraft-wise that's 179 models. Not all of them are late war or post war rides. Some of them are sold as specific paint schemes for famous pilots.
Zhukovsky's I-153-M62 is a premium Rank I Soviet biplane with a battle rating of 1.7 (AB) and 2.0 (RB/SB). It was introduced in Update 1.31. It costs 250 Golden Eagles. Golden eagles can be obtained both by purchasing them for real money and during promotional events, for winning places in contests or tournaments.
Some of them are aircraft painted in a different national scheme.
The (insert rising sun icon) B-17E Flying Fortress is a premium Rank IV Japanese heavy bomber with a battle rating of 5.3 (AB), 4.7 (RB), and 5.7 (SB). It was introduced in Update 1.43.
Some of them are just offered to include more global participation.
The Pyörremyrsky is a gift rank III Swedish fighter with a battle rating of 4.3 (AB/RB) and 3.7 (SB). It was introduced in Update 1.93 "Shark Attack". Obtained as a purchasable pack. (Pack or Bundle, aircraft are vehicles in the game that are unable to be purchased straight from the game's interface, requiring it to either be purchased from the Gaijin Store, given out during events or in promotions.)
I don't know how the game comes up with its battle ratings (AB,RB) but I'm assuming the higher the more effective it is supposed to be. AB is its (arcade rating) and RB is its realistic rating according to the wiki site (arcade vs realism as perceived there).
A rather complex 'free to play' marketing system as compared to Aces High, which doesn't rely on a micro-purchase system. Obviously AH player made skins offer players a greater variety of customization not available in WT.