The difference is that one is an idea barely fleshed out(like someone saying they want this armor and for it to do this and that[without enough explanation], but leave out all the stats, tier, obtain method etc), and the suggester's only counter to people asking for more details is "I'll leave it to them", and the other is a properly fleshed out idea, with maybe one tiny(or big) kink that someone somewhere decides it renders the entire suggestion unworthy for support.
Mind you, I've done more than my fair share of the latter, so I don't think it's that unfair.
On topic, when people deny a suggestion or consider it completely unworthy just because what it suggests can be used as a griefing tool, without even considering its usefulness to non-griefing players.