Most web sites are now designed an the assumption that they'll be accessed at high speed. For example, the HTML alone for Yahoo's home page is over 100kB. Add in images, scripts, style sheets, and such -- which are unfortunately no longer just eye candy but often necessary for viewing and navigation -- and a single page can easily exceed 300kB.
"Surfing" the web on dialup isn't practical any more. It's more like a slow paddle, hoping that the page you're trying to read doesn't automatically refresh too often.