Most people use a framework on top of JSP/Servlet which is why you don't see it in job ads. (Spring MVC, JSF, Struts, etc). However the concepts of Servlets/JSP still apply so there is no harm in learning that first.
It's kind of like how you don't see "Java Collections" in job ads. Everyone assumes you know the basics. Not exactly like that as you may never have worked with servlets/jsps directly. But if you don't understand the concepts like POST vs GET, MVC, tags, etc this is going to be a problem with the frameworks too.