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because most home users only receive information; the only things that are sent are information requests and emails. You don't need killer bandwidth for that. And since bandwidth is a limited commodity (like anything else), it makes more financial sense for both the ISP and the home user to stick with a lower uplink speed. It's cheaper for both.

having said that, you can get Synchronous DSL (dunno about cable), but it'll cost you, and it's unlikely that as a home user you'd notice any difference. For the most part, only web servers and databases require faster uplink speeds.

though I suppose higher uplink speeds might be an advantage for real-time games, like Halo or Call Of Duty or something...
 
In the case of Comcast it is artificially slower than it could be. The reasoning is that there is no good reason for a user to have a high upload, if they do then they are hacking, sharing files illegally, etc, etc.
 
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