We've set up a blogging solution for a client that uses channel forms with all the necessary fields, including an Assets field for image upload. Nothing out of the ordinary. The template is as light as you can get it, only a form and form fields. But with an Assets field as well. The client says that the solution downloads 7-11MB while it's uploading 2-3MB. Thus, making it too expensive for them to use. So they insist of using the poorly functional moblog feature instead.
I find it hard to believe that the channel form would download that much data, even more than what is uploaded! I have made data traffic measurements myself, and it shows only 1MB downloaded while 3MB was uploaded. Which is what you would assume. These measurements are pretty consistant. This particular image was taken from an iPhone, with no extra compression. I made that measurement while being on 3G as well.
In any case, what could be causing huge amounts of download traffic? The channel form is just a plain form, while the Assets do have small thumbnails showing, but that wouldn't produce that much data traffic?