ok. french touring bikes were the first to have vertical drop outs, put in place to ease wheel removal, and because horizontal drop outs only support the axle in a very minimal way, leading to axle breakage. the french touring bikes were way ahead of thier time, and colnago or cinelli, i cant remember which, were the first to reinvent, and universally popularize the vertical dropout, which again, was only used on a limited number of very high end custom french bikes. the vertical dropout has been around in this respect since the late 1930s. ostesibly old racing bikes had semi-horizontal drops for wheelbase adjustability, but its more likely they had them to ease production, and because old non indexed derailluers didnt need the accuracy of a vertical dropout. touring bikes couldnt use the semi horizontal because of all the weight carried on a touring bikes rear wheel. does that help? it has nothing to do with weight.