[rdtsc]

I guess the difference is that in one case they have to explicitly allow you in -- by issuing the visa. And in the other case, they have to explicitly not let you in (presumably by stopping you at the airport before boarding?).

[kjhgfgbhnj]

The new US online form authorizes you before you go - can't see how that is different from a visa.

[rdtsc]

Yes in that case it is not. They are just saving you a trip to the embassy and $100+.