I agree, and this has happened to me five or six times now.Where I bristle a little is when people (editors as well as agents) request material and then answer via silence. That's a case where people feel like they're left dangling, and it's kind of rude, in my opinion.
I know some agents are concerned that if they reply with a rejection, writers will become harassing and abusive. But I prefer that such agents just don't request material from me at all. That would make matters easier for both them and me in the long run.