Gary Ross, another founder of a small corporate law firm, writes in Above the Law about how lawyers should handle client inquiries about areas of law outside their specialty. As Ross notes, this issue comes up far more for lawyers at small law firms than it does at big ones, where there is usually someone with appropriate seniority and expertise to weigh in.
Clients should definitely avoid the mindset that lawyers should be able to speak intelligently about the basics for every area of the law. Law school and the bar exam cover a lot of ground, but far from everything. There is no reason to expect that a randomly selected lawyer would be able to rattle off details about, say, import/export regulation or local liquor licensing requirements, if asked out of the blue. While there are still true generalists who practice in small towns, their actual knowledge base is limited to the types of matters that generally come up among citizens doing regular things, i.e., not derivatives regulation.