Actually, in OTHER countries (think Asia), there are very large server farms that are able to deliver data at that speed, to just about everyone. The US seems to be very happy with the status quo (except for us geeks).
Concentrated population allows things that in the US just don't make sense. My brothers are a 250 mile drive in opposite directions from me here in Raleigh, NC. My wife's sisters live in Dallas and Bend OR. For any of us to hit up Google means some long hauls. Although they are going to give me a close link soon and the sister in OR will get one soon. Korea, Japan, Singapore, even AU has nice dense populations compared to us.
Well, with AT&T 6 meg DSL servnice now available out to much longer loop lengths (I am aboiut 15000 feet loop length from the CO), that will create more competition in more areas, and Comcast has to stay on top of that.
You have to remember when AT&T says "6 meg service" they still mean "Up To!" Read the fine print. Even with longer loop lengths you're still not gonna get 6 megs unless very close. The updated technology(RTs) just allows them to reach more people at beyond the old 18,000 foot barrier, not necessarily faster. Typically with Comcast you get the full advertised speed, although not guaranteed, unless you've got problems(or a not as well maintained area). DSL is still highly dependant on distance whereas cable is not.
If they were door-to-door sales people, they weren't AT&T employees. They were employees of an outsourcer hired to market the system, and the actual sales people that the outsourcer employees may or may not know the specifics for your pair of wires. Your neighborhood may bee about 15,000 feet from the CO, and the path that most of your neighbor's pairs take may be fairly direct, but your pair, for some obscure reason, may divert through another neighborhood before reaching the CO. The sales people in the field aren't likely to know about any exceptional issues. They're also paid by commission, and aren't so much concerned about whether your order will need to be canceled sometime in the future because they will have moved on.
So you may very well be able to get the 6MB service, but don't be fooled into thinking that you were told this by a "bona fide phone company employee."