I do see your point, but I guess it doesn't bother me as much as it does you. I also suspect that it's pretty easy to overestimate the number of questioners who are 'lazy' and not scanning through enough of the suggested 'related questions', although there's no doubt that happens. Moreover, I'm disinclined to vote to close questions that aren't egregious (ironically, I have done so several times over the last few days, though). Among other things, I suspect you're right that it would become a disincentive.
I think that part of the issue here is that there is an unavoidable tension between the simple question-and-answer nature of the site, and the intention to have the site build up a repository of information over time. Some of this is indicated by the discussion of how CV sees itself; there's a lot of overlap between this site and other venues on the internet. We want to build a lasting knowledge base, but a lot of new and one-time users will necessarily see this as a place to ask a simple question without thinking of those questions as something that gets stored for posterity.
In my opinion, two strategies are appropriate. I agree with @AndyW and others who suggest using comments that suggest other questions. Setting aside the effect this has on the questioner, it's been tremendously helpful for me. I can't count how many times I've gone to a question, and seen the comment '[this] question is pretty similar and has some really good answers', and then navigated over to the other question, and learned a lot more about the topic than whatever I would have said. Again, maybe that questioner never goes there, but that doesn't bother me; maybe a subsequent person ends up stumbling across the link and does end up reading the good question with the comprehensive answers. If nothing else, having lots of links pointing towards the best of CV helps Google to find the most helpful discussions.
It is definitely true that certain types of questions / issues come up over and over. Since I only know 3 or 4 things about statistics, I often end up over time with lists of questions on just a few topics where I've given similar answers. Eventually, I put together what I think of as my clearest and fullest statement on the issue. Afterwards, when those questions still arise, I can give a perfunctory answer and link to where I've discussed the topic more thoroughly. (I have also linked to other contributors' answers, of course, but I'm most familiar with what I've written.) For me at least, having tried to answer a question several times helps the ideas 'gel' in my head--I may well not have been able to give my best answer the first time. Furthermore, I think this process does tend to elevate better questions and answers over time, and is part of the resolution of the tension I mentioned. I guess what I'm saying is that I think the process is actually fairly healthy and organic, even though I can appreciate the frustration in the interim.