CS as a subject has more scope of tricky questions.. it is more involved in a way.. :P
i may be wrong as i havent studied other streams, but streams like Mechanical might have direct concepts and questions.. Once you know the concept, i think one can directly answer questions for Mechanical/Civil..
But in CS that is not true.. For e.g In Algorithms, the concepts remain same, but questions can be made very tricky and require a good amount of knowledge and practice to crack the tough ones..