How long does the JC2 distribution actually take? (Just Cause 2)

Having bought a game on zaka-zaka for 100 rubles (and, by the way, there is probably no difference where I bought it) - at a gambling store, gama-gama, gameray, gamazavr, or in the incentive itself - I got a key, passing it through steam, they gave me Just Cause Retail, all DLC and multiplayer access.
Having started downloading via Steam, I was very surprised by the download size - 3.9 GB.
On disk media, the game obviously takes up more.
Who can tell you what the trick is?
Is content loaded from Steam as it progresses?