DS7 had 19s on the working memory wisc subtests. His comprehension was slightly lower but still quite high. He absolutely has social issues that affect him on a daily basis, so I wouldn't say that all kids with ASD issues would score poorly on comprehension. The nature of the wisc comprehension subtest is to answer about the practical or usual course of action is in a specific situation. For example, "why do you wash your hands".
One reason to score less than amazingly is just being concise. For example you could answer with, "I do it to keep my hands clean" and then not follow up with any additional explanation. Or someone could go into detail about the demands of living in a community, or over-population induced epidemics, or bacteria, or all of those things. (And while the first statement may be really a summary of the second, the second answer likely garners more points). This is how I think my DS must have achieved a higher end score on comprehension, just going on and on until the tester told him it was time to please stop. Because it certainly was not from some intuitive (or learned either) grasp of social convention.
Not appearing amazing in math to everyone at this age is not too surprising and can be a reflection of schools' focus on operations. When I think of math ability it's the ability to juggle symbols and infer relations and follow a line of logic, think dimensionally, and so on. Very different from school math at age 7 or 8, which is more about quickly adding and subtracting small sums, maybe multiplying which is just more adding, possibly dividing which is more subtracting, etc.
