Some visitors download index.html BUT No GRAPHICS. Why?

My home page index.html file is often downloaded, but with no graphics. Index.html seems to be fully downloaded, looking at the be highs?yte count. Why do they do this? They don't seem to be robots, spiders, etc. Do they have cached images? I worry a bit because they don't seem to show as visitors (or on heatmaps). And are they counted by AWStats, giving false highs?

[email protected]

one less conspiratorial reason is: you have a cool site and they're scraping your code to see how it was made. I've had this occur to products and sites I've worked on.