It's a handheld computer. You can certainly argue against having the right to customize it, but there is no technical reason you shouldn't be able to. It's not a toaster.
You can customise it, just not arbitrarily.
I can change the display format for the time in the status bar, but I can't have an animated kitty running about up there, as much as I'd like to.
Reminds me of a tiny thing on my jailbroken device that pleases me: http://i.imgur.com/1QXUm.png - every slider is an animated kitty. (It's called NyanSliders in Cydia, in case anybody else would like it, and I think there's an unrelated version of the same concept available for Windows too.)
Hey now ... that's not fair to us toaster hacking people ... we too like to enjoy our modified toasters.