That's because ISPs game SpeedTest.net and give you your full bandwidth for the test data. So the 350-500 is more accurate to your actual milage (at least for Netflix's peering agreements).
That would be totally valid, except I get a perfectly fine and stable 500 down from, for example, Microsoft's MSDN, depending on the size of the ISO showing this straight for a couple of minutes..
Right, this tool only tests your ISP's speed for Netflix content, which most tend to throttle. For the majority of people, Netflix is the only way that the saturate their bandwidth, so this tool is more relevant to them than to people downloading ISOs. I generally speed test by wget'ing a large ISO because those numbers are more relevant to me.
Different paths will have different amounts of bandwidth and latency, especially at different times when some parts of the network are heavily loaded.
In certain cases (ie: transatlantic cables), there is only one quick path between US and Europe. If that cable is heavily loaded, then your bandwidth when talking to a European server will be slower.
