There is a difference of intent.
If a question is off-topic, that is akin to asking about tea on
coffee.stackexchange.com. It's a blatant, obvious violation of the parameters of the site. Now, you could argue that users simply don't read, and I will agree with you, but ignorance of the law is not an excuse. But in this case, it is egregiously off topic. That is, even the most casual browsing of the front page would immediately let you know what is and is not on topic without thinking too hard about it.
When a question is not constructive the distinction is much subtler. It can take a bit of trial and error to "get it". I also believe that many unconstructive questions do NOT indicate the same level of obliviousness bordering on irresponsible failure to just look at the questions on the homepage and ask something similar. I believe it is possible for some people to honestly try to read the faq and still get it slightly wrong.
Therefore I don't support this.
(However I do think that egregious examples of unconstructive questions should regularly be downvoted and remember, downvotes on questions are now free... Should downvotes on questions be "free"? )