because wikianswers is a place where people around the world answer questions and they might not know the answer to the question or it's never been asked before.
Infinite
4,622 and counting
WikiAnswers doesn't 'block' inappropriate questions, but rather stores them so no one can answer an inappropriate question that has already been asked. It is called a 'Catch-All', and it stores all of the inappropriate questions so when a user types in an inappropriate question that has already been asked and merged into that Catch-All, they will get an answer telling them that inappropriate questions are not allowed on WikiAnswers. In a way, WikiAnswers does 'block' inappropriate questions.
WikiAnswers has a category called 'Most Amusing Questions Ever Asked on WikiAnswers'. The category is home to many amusing questions that also goes under the category strange, unusual, weird, etc. Below is the link to the category.
The number is in millions and it keeps increasing every day
If there are no questions on a particular topic it means that the questions have yet to have been asked. WikiAnswers is constantly growing and evolving so there will always be some topics or questions that are not present. This will decrease as the site grows over time though.
If your Questions have been answered than wikianswers will send you an email.
WikiAnswers does alert you when a question you asked has been answered. At the home page and on question pages, the bell used for notifications at the top-right of the page will have a red notification box to let you know about questions you've asked that have been answered.
"Enter a question here" is the box for you to ask your new question on WikiAnswers, or to ask questions that may have already been asked and answered.
Glad you asked! Though people have different reasons, my experience is pretty common. I asked a question in Google search and WikiAnswers was one of the search results. I asked my question on the site and while I was waiting for the answer, I started answering questions. My question was answered pretty fast, but by then I was totally hooked on the site. That was in 2006 and I've been here since.
As of August 13, 2013, there are 19,591,633 questions that have been answered on WikiAnswers.