Geez, where the heck did I say I wanted unlimited drops ? I'd rather suggest the same system as for items in TF2, so that you wouldnt get all the cards just by idling for some hours, and as far as I know, the trading system in TF2 is well alive.
The only difference is that the variety of cards is way lesser than in any real life trading cards game or even than in the TF2 item system. Moreover, you need to buy cards compatible games in order to gain a mere couple handful more possible card drops : the comparison with booster packs is invalid because those contain sensibly larger amounts of cards for a far lower price than a fully fledged video games (even if, obviously, some indie games are worth way less than packs from popular trading cards games).
There is also another obvious flaw in that reasoning in the way that booster packs offer a big amount of certain cards, whereas purchasing more games may yield you a very partial amount of the cards you'd ever need.
I mean come on, in order to even participate in a realistic trading metagame, you'd need to spend hundreds of dollars/euros/whatever your currency is in order to have a card pool that really justifies a need for trade.
Also, please, the argument about profit for the developpers is not sensible at all : the profit they're going to make from the cards is clearly negligible. Moreover, saying that no devs would ever make cards anymore because of a lack of profit implies that it costs a substantial amount of money to make them, which certainly not the case, aspecially when it comes to the Killing Floor cards, as demonstrated by
this thread showing cards made singlehandedly by a lone fan for something that certainly amounts to maximum 10 hours of work, which is nothing in terms of graphical artist salary.
To conclude, I'd also like to point out that all comparisons with real life offer and demand systems should be handled with care, as we are dealing with a product with absolutely no production costs, sold at arbitrary prices by people of low economical awareness and inside a market designed to be explosive with more than one single acquisition scheme (which are random free obtention or overpriced acquisition on a third party source).
As n2spd said, you're probably missing my point and what the hell, if I said Nova and retromenace were butthurt, it's because of the atrociously mean tone of their replies, implying dishonest behavior from my person based on virtually no knowledge of my character. As a matter of fact, I welcomed the trading cards system with a warm heart because it would have given me an incentive to play some of my games which I was neglecting, would it be because of boredom or because I had finished it twenty thousand times already. But then I discovered that it was pointless to play for more than a couple hours due to the 5 cards limitation, ergo my statement.