DSL is BELOW the standard in many countries, namely Japan, Taiwan, and Sweden. Moving to DSL WOULD be a significant move forwards, but such an investment would reap practically no benefits in the visible market. Why? Well...
For 1, from an economic perspective, how is such an investment justified? All the buying and selling that goes on online doesn't NEED broadband. The reason I switched from isdn to adsl? To download stuff faster of course! The introduction of broadband across the entire united states will somewhat increase the amount of illegal activity that goes on online. This will, in turn, decrease the overall level of aggregate demand in the american economy (due to the emergence of black markets online). This is by no means a bad thing. The US is already terribly in deficit (balance of payments wise), so by advocating the wide-spread use of broadband, Bush might be counting on the fact that it'll decrease the level of AD in the american economy. Less AD=less inflationary pressure on the dollar (demand-pull inflation at least). This 'might' be a bad thing as it might increase unemployment (by the phillips curve, since employment tends to be inversely proportional to inflation). It might also be a good thing as it might stabilize the American economy (though this might well be through a recession).
Furthermore, investing in the internet is sort of an investment in infrastructure. The internet forms a really important part of a country's infrastructure, so by attempting to improve infrastructure, bush might well be trying to pave the road to economic growth.
ehm...
oh, and dsl and cable both have their merits: cable tends to operate faster (larger pipe capacities), though if more people use it, it slows down. DSL on the other hand, tends to be slower, but it isn't affected by the number of people using it....and there's also a marked distinction between DSL and ADSL...