No, they are not the same. 70-492 is a "sum" of 70-486 and 70-487, so you need to have the knowledge of *both* 486 and 487 in order to take 492.
70-492 is the way to go if you are already a Web Developer 4 (which requires 4 exams, not just one). But if you are starting afresh, then it is shorter to get the MCSD by means of 480 + 486 + 487.