I don't see why they limited them in quantity if they are unsalable. Seems like a 24 hr offering would make Innogames far more money, and squelch at least the complaints of those who want to give them money for these items and can't.
Edit: for those claiming that it's not fair to those don't pay for premium, I respectfully disagree. This is a free game, the option to pay for premium content is a given, and is a trend followed by most free online games. If you want a truly level playing field where all players have the same opportunities, you usually will only find it in games that you buy (example: WoW).
In the end of the day, it costs money to create, host, and maintain any "free" online game such as this. Those costs go up as the quality of the content and the quantity of players goes up. When I last looked I did not see the interface covered with ads, so it is premium content that pays the bills. Instead of complaining about players that pay for premium, you should thank them for keeping the lights on so you can continue to play for free.
(I'll climb down off my soapbox now)