You mind if I chime in?
That workout you mentioned (400/300/200) starts out as Int. Tempo with his times, then kind of borders between Int. Tempo and SE2 workout.
That is a very good workout in the early season for building work capacity as you have mentioned and also to mentally get you ready for the season to come.
They might help benefit a 100m sprinter by just whipping you into shape, and speed endurance. Look at people like Dwain Chambers (I believe that's who it is). He thinks the 100m is a long race. (Loser!). Give him a workout like this and he wouldn't think that anymore.
Another thing is, when using this at the end of the season, it can help condition you to run rounds. Like for Carl Lewis, he had rounds of the 100m and Long Jump. It's great for getting you physically and again mentally prepared.