The laziness issue is something that appears to be common in athletics, and particularly in sprinters.
There is no reason why Usain Bolt couldn't also run the 400m. After all, it is common in swimming to see swimmers compete in the 50m, 100m and 200m freestyle, in fact Pieter van den Hoogenband managed to win medal in all 3 distances at the 2000 Olympics - which would essentially be the equivalent of someone winning the 200m, 400m and 800m on the track given that swimming is roughly 4x slower than running. There are even more swimmers who specialise in the 50 and 100 and would jump at the chance to race a 25m race if it existed (which would last about 10 seconds - so the equivalent of the 100m sprint on track). Scaling up distances is done in swimming, why is it never attempted on track? Ian Thorpe managed to be world class in every distance from 100m, 200m, 400m, 800m and 1500m.
You may argue that swimming is a vastly more technical sport than running, which would be true, so perhaps that is why - ie the person with the best technique will have a massive advantage inherently regardless of their physical attribute.
Jonathon Edwards is another sprinter who was deemed to be lazy in training, he would literally refuse to run more than 100m repeats during training. Usain Bolt runs up to 600m repeats. Edwards is also another athlete who could have done multiple events but didnt bother. Edwards really should have been the first white man to break 10seconds in the 100m, he would have probably had a shot at winning the 1992 Olympic 100m if he bothered to run and train for it - his PB would have been good enough to get in the final despite never running it properly. His max running speed has been measured at 11.9m/s.. Usain Bolt's is 12.3m/s. Yet he didn't do it, why? He probably could have entered weight lifting events as well if he wanted too... Although you may argue that he is justified given how good his WR is in the triple jump.
Instead of braking 10 seconds, he left it to Christophe Lemaitre to be the first white man to do it last year. I think he is also the youngest man ever to do it (I think he did it at 19 or about a week after he turned 20). He has already PBed this year again at 9.96, and given where other sprinters are in their times you have to wonder whether there is a possibility he could take a significant chunk off that if he tapers for the world champs. But even if he doesn't, it isn't unrealistic for him to take off 0.1s by London 2012 to be down at 9.86 and start getting into the territory where he can run sub-10 with his eyes closed, which would mean he would be in a great chance of making the final in 2012, then anything can happen... but no, he just wants to run the 200m and the 200m only. Why? He is still only 20 so anything is possible by 2016.