Maybe the ticket you bought was non-refundable from the airline but in view of the circumstances instead of just losing your money, they have given you vouchers for the next time you fly?
Expedia might have gievn you vouchers becuase the ticket was none refundable like Dassie said. But I beleieve they gave you vouchers so that next time you book a holiday you spend it with them, this way they are not losing buisness.