At this stage of the beta (currently, the private beta), we're still trying to define the boundaries of what is on and off topic. Close votes for off-topic questions are a good way to do that, but they don't impart that much information, and they don't provide very good precedents. At this stage, it's much more useful to get discussion out in the open about whether and why certain questions should be closed, so we can come up with good rules of thumb about certain circumstances, and when people wonder in the future why their questions are being closed, we can link to the discussion demonstrating the community consensus.
The SE close/reopen system is somewhat weak; it only gives a way for people to support keeping a question open after it has been closed, and it leads to back-and-forth close/reopen cycles for debatable questions, since it takes only 5 votes either way to close or reopen it. A thread on meta with well-thought-out arguments, and an answer voted to the top by the community, can provide a much more definitive answer, and can help come up with a rule that can be applied more generally.
So, please, at least leave a comment if you are going to vote to close, and preferably start a thread on meta (and link to it in a comment). Of course, if something is obviously and blatantly off-topic or trolling, you don't need to do that, but for questions that are closer to the grey zone, this will be very helpful for the future.