I for one love the exclusivity in skins. Also I'll make it clear now that I don't own the bundle (hell I don't even own Annie, she's one of about 20 champs I don't have).
The reason I like exclusivity is because it adds more flavour and interest to the game, I like the fact that if I'm going against an Annie mid and she has the Goth skin, I can estimate that maybe she is a die-hard Annie player that shelled out just to get that skin. I'm then more interested to see if she's really good.
I bought the Headless Hecarim skin because I liked it, but also because I like to think that if Hecarim becomes FOTM, my team will be able to see I've been a fan of him for a long time and I'm not new with him, as I must have had him at least since October.
These experiences might not mean a whole lot, but I think they add interest, and if you make the skin available to all it kind of kills that interest. After all there are hundreds of normal skins that are available 24/7, I would rather have a few exclusive skins for die-hard fans of that champ and a whole lot of great other skins available to everyone, which is what we seem to have now.