When I scroll down a web page the scroll bar appears and constantly changes size as I scroll What does this size relate to?
Some websites load new content as you scroll down the page, to prevent new page requests thus reducing bandwith. i.reddit.com is one off the top of my head, the Market app does this also.
The scrollbar is related to the size of the content of the webpage you are looking at. If it the scrollbar is changing size, then that means the content on the page is likewise changing size (via asynchronous calls that retrieve more data for that webpage as you are browsing it).