Not all DSL rechnologies are created equal. Not all providers are created equal. Oversubscription rates, actual bandwidth, and other factors make a major difference in the quality of the connection. DSL and dedicated digital services are not created equal. The tachnologies are radically different in delivery and behavior, and are treated accordingly.
Distance is a factor in a major way.
There is no need to rehash this point because it has been discussed before at length, plus it is fairly straightforward. Suffice it to say that not only is it not universally available, it degrades the farther from the CO you are. When you start piling more sophisticated network related items on the link it can bog down or misbehave. DSL can have cost factors that users do not anticipate. I know quite a few ISPs that will allowbetween 1 and 3 GB of transfer and start charging once it goes above that.