Not really all that impressive. I wouldn't buy a 4S now either. Now if that said total sales already exceeded 4S sales then I'd be impressed. But if you want an iPhone you already have one or are waiting for the next one.
I sold my ~10mos old white 64GB 4S a couple weeks ago for $650, that should tell you something about the iPhone. Whereas if I decide to sell my ~2mos old Samsung S3, I'll probably be lucky to get $400.