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These are just my opinions but...
I find such replies unprofessional. I don't think that the fact that it is a forum reply and not direct customer support reply by e-mail provides and excuse to be informal and unprofessional in communication. Regardless what customer types here (I'm not talking about trolls but customers).
Also, often when someone asks the question you reply that it is already explained somewhere in the thread. People don't have so much time to browse through hundreds of pages of forum to find the answer. Nice and professional way would be to either copy the answer or provide a link to the post. Sometimes when I read your replies here it looks like you are talking to some pub buddies not customers