Interesting question Laura L. I confess I have not studied the RW schedules, but I think you're right to question the value of short intervals (eg, 400m reps). There is a considerable evidence that the key to improvement in distance running is to increase one's lactate threshold - ie, the speed at which you can run without flooding your muscles with lactic acid. The way to do this is to train close to threshold speed - eg, tempo runs, long intervals. Short reps (such as 400m) are of less value. Not so sure about hill sessions: long, sustained hill efforts are probably worthwhile, whereas shorter hill sprints won't be so beneficial.
But as you suggest: the real key to success is sustaining your training over a long period. Pulling a muscle because of too much intense speedwork is a real risk.