While using a previous ticketing system we had things configured so that user comments would re-open tickets as described above. However, this proved extremely problematic due to users sending 'Thank you' comments after we closed out issues. They were being polite, but in so doing were creating extra work for us since we had to go in a second time and re-close the ticket.
I'm not opposed to this functionality being added to BOSSDesk, but if it is then it should be something we can turn ON/OFF as needed, so that each administrator can configure his system in a way that works for his user base.
Oh, and sniderge is correct: Users do have the ability to re-open tickets manually if they need to do so.