I apologize for having to revert your change to the Steam icon. I actually quite like the design, but all other storefront icons at present are square, so the circle design doesn't fit our current aesthetic. We can discuss changing it if you'd like, but it was actually unintentional for anyone but admins to edit site-wide icons like that. We apparently forgot to protect them, which we've fixed to ensure people can't replace the icons with, uh, obscene images.
If you'd like to propose any changes to our current icons, you're more than welcome to do so in the Forums. We try to minimize bureaucracy as much as possible so that as many people can add to the wiki as possible, but we also want to make sure site-wide changes are approved before they're made so we don't have people acting independently against the majority opinions of the community.
You're obviously talented, so if you're interested in working on our icons with me I'd love to have you on board! I'm our lead designer at present, and it gets rather lonely being the only one here with any design sense ;)
Thanks, nicereddy