Bunnies > imps? *grins* Its the fuzziness and the wigglie noses. *grins* Maybe the optical blinding factor.
Seriously my guess is because its a weird hue. If EA had made them just like say ranger-green in hue I bet they wouldn't be anywhere near as wanted by many. I haven't sold dozens or anything, just like four. I don't pretend this to be the price for everyone, just saying my personal experience to help provide additional info.
Edited to add: On the imps I would honestly seek out the rp community on your shard. I know my guild use a lot of animals in rp plots and I'm sure other evil guilds might be willing to shell out a few mil for one of the imps, maybe more.