There is bias, but I think this is because of the demographic that are attracted - scientific and technically literate; but not generally philosophically sophisticated.
This is why for example the site attracts a disproportionate number of questions on logic, and this mostly on various flavours of formal logic, but not philosophical; for example I've not seen any questions on Priors tensed logic, or Hegels onto-logic; and why some of my own pointed questions on Parmenides and Zeno which is to defend Hegels onto-logic is possibly misconstrued as an attack on formal logic; or on science itself.
I've only noticed (on the whole) that poor-quality questions have been closed:
Sometimes this is because there are too many questions in the question, and for this reason there is insufficient coherence; in which case one ought to ask several smaller ones;
Or questions are not using philosophical vocabulary appropriately, in which case the question ought to ask how it should be deployed;
Or questions are asked in which the substance has been submerged by style (this is tempting when one admires a philosopher with a certain style) in which case simplify: it's far better to ask the good simple question hiding behind a complicated one; and one should recall style is achieved in combination with substance; and is never as easy as it may look.
Or questions lack reference to the philosophical literature; ie how a certain word is used, say sovereignty or absolute by Hobbes.
Because of the high ratio of inefficient questions in the above senses; at one point I would try to extract or find a good question in them; but on the whole I found this bad practise, as it only appeared to encourage more bad questions.
For example, I don't have anything against Nietzsche; but I recall when I first began on this site that most questions on Nietzsche invoked 'The Superman' or 'The Herd' - these would be his own disciples that he warned against; I'd be interested myself on seeing good questions on Nietszche specifically focused on his texts.
It's also, I think because of the demographic attracted that we don't get many good questions from the continental tradition: ie on Levinas, Gadamer, Kearney or Foucault.
The real question is how to encourage breadth and diversity; depth and focus.
Personally speaking, I don't have any formal philosophical training; but I tend to judge questions by the tradition in which I have been trained - mathematical and physical - but this not in a literal manner but by analogy, so similar standards of diversity, coherence, style, focus and reference to tradition.