I am not arguing with the facts - everyone knows that. That's my point.
I'm saying this isn't the case at all as it depends how you train.
I train at 95% of my max HR and can do a 20km TT without breaking a sweat.
I then struggle over races 100km+.
I'd have to agree 100% with bruiser. Training in zones 2 and 3 will improve your core fitness and aerobic capacity. While training in zones 2 and 3 you can also concentrate on technique.
Training in zones 4 and 5 will improve your sprinting and boost your LT.
How you train
influences the balance between slow twitch muscles (requiring less energy and better equiped for endurance events) and fast twitch muscles (requiring more energy and better equiped for sprinting and fast short distances).