webpagetest actually renders the document and all referenced items. It's more similar to what firebug/yslow will tell you, and very useful for designing a site to load quickly.
I'm not sure this is a metric a web developer should care about. I always assumed the website would deliver the same X bytes of data, at the same level of performance for each request, regardless of source location. If this, or any other test says your site is slow from a particular location on the net, what can you possibly do about it? You aren't really measuring your web site performance you are measuring the quality of the pipe in between the two sites, something you have no control over.
"If this, or any other test says your site is slow from a particular location on the net, what can you possibly do about it"
Basically it nails down to reducing the number requests and the roundtrip time per request (aka latency).
- Use a CDN to reduce latency (e.g. cachefly, cloudfront)
- Outsource some javascript libraries (e.g. jquery) to google's CDN
- Move servers closer to customers.
