Hm. Perhaps it should be added to the sticky request guideline thread? In most cases it's probably just a polite gesture to reply, but sometimes you might be forced to keep your schedule open because you're not getting an answer, and during those days you could potentially have taken another commission if you had just received a "no thanks" right away, causing a loss of work opportunities.

@AceStealman, if you're still reading this thread, the above wasn't directed to you in particular, just a general thought.