Why wait until fall? Who knows what will happen then? Prices may be higher! Today is a great day to buy a Prius!! Spoken as a true chauvinist.
That and I think Toyota is somewhat forced to due to the Japanese yen being way too strong vs. the dollar. See USDJPY=X Basic Chart | USD/JPY Stock - Yahoo! Finance. The strong yen has been really hurting Japanese automakers and they've publicly stated it many times.