It is somewhat common for a question to be off-topic because it is too bug-report like. This is certainly a legitimate reason for closing a question. One problem, however, is that unless there is a way of subsequently adding a link to a bug-report, the (closed) question is useless to anyone who might stumble across it through AU or search-engine searches. Take for example this questionthis question.
It would be much better if anyone (not just the OP) was able to link one or more bug-reports to the closed question, while not being able to add additional comments/answers. This way if a bug report were to be created later which happens to match the AU question, a link can be added, making it easier for others to find the bug-report and contribute to it.