'Cause the straight lever is pre-'78, and less common these days. There is an exception here with the Campag releases... They made a rare curved release that looks otherwise just like the straight style version...supposedly for track use. Also, it wasn't uncommon for racers to put a curve in their straight releases prior to '78, and if well bent, they're cool too. BTW- lever forging for earlier straight levers reads Campagnolo in block letters; post '78 curved release levers are in script.