While it doesn't apply to every case, the way you phrase a Google search can have a big impact on the results. Probably half of the time that I'm in a situation like that, they did try Google first and it simply didn't return any useful results. Before discounting them, consider the possibility that what comes naturally for one person's search terms (even when it does seem really obvious) isn't always what other people come up with. So when I answer a question like that, I usually try to include in my response what I put in the search bar and why (if it's not clear).
A good example is the "how do I ..." search phrase for questions; it seems an obvious first search try nowadays because it's so common, but definitely was not always this way, especially if you've never used it before. The corollary is true as well, sometimes "how do I ..." searches return no useful results, but simply entering a few key words relating to the topic / question will; and knowing which keywords to choose and how to phrase them is an acquired skill.
I tend to think of it as, if the question is that easy to Google search that the answer can be copy-pasted, then why not help out just in case, since it takes such little time to do anyway. And if it's one that's slightly more in-depth, then the odds are even greater that the results they found didn't answer their question in the way they were hoping, or that they were unable to find one, and that your response would be helpful to them. In either case, showing how you found the answer helps them learn how to do it better next time; "teach a man to fish".
That and the fact that StackExchange is pretty common to see on the search results list, so your answer might help other people too if Googling a similar question, sometimes years down the line.
[wiki](link)it states <blah>, did you miss this in your initial search?" Sure, it's a passive way to say "do your homework", but it comes off less hostile/elitist. There are people on the other end of those questions, and on Arqade it's safe to say the average demographic sits below the drinking age, meaning a lot of them are still in school learning how to cite sources & perform research.