This very topic came up in a recent discussion when making some decisions about what sites a client is developing should be made for 800x and which ones he might consider going to a layout that fits the 1024x presentation. What it came down to is

1. the niche and content quality (bought vs exclusive and hi res/dvd quality vs med/low)

and

2. what countries would be the primary marketing targets/buyers

If you're producing your own content, and streaming DVD quality videos, and offering hi res photos, you're obviously targeting people that have a fast computer system and a broadband connection. If they have that, it's very likely they also have 19" and up for a monitor. Designing something to look good at 1024x becomes a very sensible approach under these parameters.