Steam Invites/Gifting - A social side to gaming?

Now I'm reasonably new to the whole steam concept, since deciding to check it out from the amount of times it was mentioned in lectures. Since finding a few friends and cruising the store I've realised how much of a good thing the've got going on. Awesome specials, informative news and community discussions (reviews and all sorts), driver support, and best of all game invites.

I've just been recently invited to play Dota 2, which usually costs $30, and needless to say I downloaded it immediately. Theres something about getting an official top-rated game for free that just made so much sense to me, I mean with the amount of video game piracy these days game producers are struggling to meet profit margins and hence whacking a giant price tag on new release games, which sends me running even faster to torrent-ville. By allowing a certain amount of gift invites to friends it increases the activeness of the game, word of mouth spreads like wildfire, and piracy would definitely decrease in my opinion. Whats more is that, this gifting would return itself, and a cycle loop would flow around a group of friends gifting each other new releases.

Needless to say I think its a great marketing tactic and wondered why this hasn't been around earlier?! Or maybe it has and I've just been completely oblivious to it?