It might seem like they're all the same but, before you even get to the myriad components, if you look at just endurance class road bikes, for example, while you'd be correct to expect taller headtubes compared to racier breeds you still find that fore and aft angles are different, wheelbase and chain stay lengths are different, effective top tube lengths differ, BB drops aren't all the same, there's every kind of tube shape from simply round to big, swooping, highly tapered oval-tangular tubes; and, unlike the slope of a top tube, all of these details have an effect on the fit and feel of the bike. I thought I was living through the renaissance of road biking during the 70s and 80s but I think there is more happening now than ever at prices that anyone can afford.