Just saying you can't take a loan and say I will only repay the principal because 0.1BTC = 0.1BTC 
Exactly how are donations comparable to loans? They're not.Lauda's point is that fiat value is irrelevant (I agree), mine is that time factor(/opportunity cost) should be considered.
Changing the required amount at this time would be unfair to the people that have previously donated.if I already knew bitcoin then and part of this forum and bitcoin was only $10 I would have donate 50 btc because it's worth to be a vip of this forum but I guess it's almost impossible to donate $50 now..
Why would it be impossible to donated $50? You can donate any amount that you want, just don't expect things in return.