When I post something, it moves down the pages fast. Does it jump back to the top on an edit, comment or answer?
Most people find questions they would like to answer based off of the tags your question has rather than it's position on the page.
If you question is good and upvoted, it will appear farther up some pages such as the "Unanswered" section. Also the community crawler will occasionally bump questions.
You can bump a question when editing it. Search for questions here on meta using "bumping" (here), some considerations have to be taken for it as it is easily abused. It is also considered editing when you retag a question. Commenting does not bump the question, but answering does. Other than that Coyote already pointed out the community crawler.