If he averaged 32 starts per season over the 20 seasons they have him in he would make 640 starts. 442 decisions out of the 640 starts would still leave him 198 ND for his career.
Consider Tom Glavine made 682 starts and had 508 decisions, thats 174 ND. Strasburg would have 24 more ND's in 42 fewer starts based on those numbers so it may look like a lot but it seems average.