> I'm not sure why they limit the upstream so much.
So that you don't run a data center from your house, which would saturate the network, which they are likely overselling, and so you don't cannibalize from the hosting services they would also be happy to sell you ala carte.
Also, in general web usage, the UPstream data requests are usually much smaller than the DOWN. E.g., "GET http://youtube.com/video" is very small, even with headers and whatnot added in, compared to the size of the video returned. It's more like 100:1 than 100:20, so unless you're trying to run services from home, you're likely coming out ahead.