Wouldn't it be better if there was no option to delete a question that cannot be deleted? Why is there a link there to delete when it cannot be used?
One advantage to showing the delete button regardless is that it gives you more detailed feedback on the reason you can't delete it. For example a while back I posted an answer and the first half solved the OPs question, so he accepted it but the second half contained something false / misleading as pointed out in a comment.
Unfortunately it was when I was heading off to bed and the next morning a better answer had been posted so I thought I might as well delete mine and got something like "an accepted answer may not be deleted". That was clearer than the delete button not being present and I knew to edit the incorrect part of my answer rather than delete it.
Also as Olin pointed out in a comment for Meta posts it's best to mention a particular question or answer you have in mind if you're after a specific reason on why it can't be deleted.