KenB - 5:05 am on Feb 27, 2010 (gmt 0)
My site doesn't sell stuff, it is an informational/content site. Here is my theory:
Dialup users are used to taking things slower. As such they probably tend to look around a page more while it is loading. In my case, the content stuff loads very quickly so users can get on with reading while everything else (e.g. ads) load. Being as they do tend to take things slower and look around more. They may be more apt to visit more pages on a site, especially if it loaded in a reasonable time frame. Looking around more might also mean they have less ad blindness.
Broadband users on the other hand are less patient and jump in and out of sites very quickly without looking. If they don't see what they want instantly they jump back out rather than scrolling down the page or looking around a little.
I have no idea if this is true or not but it seems reasonable and I do notice the faster the Internet connection the lower the pages per visit and lower the eCPM.