If I'm not wrong these lottery ticket prices are fixed in USD so since we are buying these lottery tickets from BTC, the prices of each lottery depend on BTC prices. If BTC prices go high then you pay less BTC for each lottery ticket and if BTC prices go low then you need to pay more BTC to buy these lottery tickets.
Probably, if Bitcoin will start to rise again, Freebitco.in will have to consider making price of lottery ticket less than 1 satoshi (0.5 Satoshi). Otherwise, it will be to expensive to buy and there will be less interest in lottery.