[nostrademons]

Well, that's usually a security feature so that hackers can't harvest valid accounts by trying e-mail addresses and seeing what the error message is. It's stupid if they can do that anyway via the password reset form, though (although presumably, if you get the password reset e-mail you'll have an idea that someone else is trying to access your account).

[goldfeld]

Or the reset password form can simply say an email has been sent to the relevant address, regardless of whether said address actually exists in their database. I've always suspected this is how most of them work.