I think that's a dangerous precedent to set, although I don't actually disagree with your intentions.
Creating questions with answers that are guaranteed to contain an explanation of why the question doesn't relate to Drupal, and can't be answered here, seem to be the wrong way round. If the question is off topic, in my opinion we shouldn't be encouraging people to ask it by providing them with a "this isn't a Drupal problem" type answer.
The question should be closed as off-topic, and moved to an appropriate site if possible. Then anyone who comes across that question on DA will be automatically forwarded on to the correct place for it - keeping in line with the mechanism used on every other Stack Exchange site.
But I guess this is part of a bigger discussion. For me, I'm not really sure why the fact that this is a regular request from clients has any bearing on whether the question is on-topic for the site. My understanding is that questions should be taken on their own merit, without consideration of external factors.
But maybe that's wrong, maybe this community needs a departure from the proven SE model to continue to thrive. I don't personally believe that but it's certainly worth talking about.
I think any major shift in the SE philosophy for Q+A (which is what we're talking about here) should involve the higher-ups as part of the discussion. We need some guidance on this, as everyone seems at cross-purposes with what sort of questions are acceptable here at the moment.