The problem is you didn't directly address the problem, you made a general statement to everyone. How would the offender know he is doing wrong when there is nobody to tell him otherwise. Also I really think you're taking this GM thing much too hard. It isn't like this is some job, although you were tasked with keeping this RP up (which you are doing well at) I really don't think threatening the RPers no matter the reason is a good thing.
Also the posts have not dropped since this RP has opened up.
Also don't confuse laziness with prioritizing. I neglect to edi because I'd rather not put time into something that I don't consider very important (it's fun, I like it, but just like I wouldn't waste time in a video game trying to do perfect strategies when my strategy works, I wouldn't go through editing here when my point gets across.)
The post did come off as threatening and demanding, even if it wasn't meant to.