Actually I have ran a website where you could replace every smiley image with one of your own and you could even create new ones ( by entering code on one box, then the image url on the right side ) ex [ ^.^ ] [url here] could come out with a smiling chibi image
I think its a good idea to make them replaceable/delete-able to help make the forums as interesting as possible
Plus something in the profile that you can check off to disable smileys when that users makes a post
like lets say If I don't want smiley faces to show up in any of my posts that the website uses, i could just check a box in my edit profile and BAM, done! now they don't show up anymore. I have seen that before as well!
So lets say i wanted to replace the originals with these, it would replace them with something more accustomed to my own taste giving the maximum customization that you can offer! (check spoiler)