Maybe somewhat difficult to understand (not too technical just not extremely articulate

but I'm glad someone finally explained the online cdkey thing.
People never shut up about "Why doesn't this keygen make online keys??"
The answer is obvious but they don't really get it.
Funny thing is that it's quite simple (if you know how) to find online playable keys, if you write your own keygen.
You have your keygen use a load of open proxies in a rotational manner to brute force check cdkey after cdkey with the master server for that particular game.
Your proxies will get banned, so you need quite a few of them.. But you can typically harvest 10 working keys with 100 proxies (depending on the game that is, as they all have different algorithms with a differing number of "real" keys and "fake" keys.)
Of course if this became a commonplace thing game companies would wise up and correlate the data access (hmm, 50000 invalid cdkey checks by this IP, and 1 valid.. let's ban that 1 valid cdkey he found).. But that's yet to happen to me so far =)
Happy hacking, game cards are pretty much impossible since like you said they are activated when the purchase is made, and deactivated when the card is used.