Nah. I think that all website's do upload them transparent it just depends. If you have saved it as a .png then you will get a great quality GFX piece but the site automatically filters in what is missing. It transparent just has a filter in there.
But I found out that saving as a .gif does actually make it transparent BUT ( and a big one) IT doesn't give a good quality and the edges on the transparent part are all rough and pixeled. Though there is no filter, its not a good option.