What Alton demonstrated was koshering, which is a similar to, but not quite the same as dry-aging. I believe he did say that he was koshering the duck, not aging it.
Koshering is a process where large grain salt (e.g., kosher salt) is used to draw out and 'purify' the blood of the animal and is part of Jewish dietary law. IIRC, fowl are excluded from the requirement, so in this case he was koshering the duck solely to reduce the moisture content and dry the skin.
Salting meat for cooking (as opposed to preservation) has become more common recently. I don't recall the name off-hand, but there's a restaurant in the San Francisco area that specializes in salted meats, fish and fowl. The main difference is that the meat is only salted for 2-3 days, then cooked. The salt protects the surface from contamination and draws out a lot of moisture, concentrating the flavor. The surface of the meat must be dried thoroughly and kosher (or rock) salt is used because the grains are too large to dissolve and be absorbed by the meat. If the meat is real salty after koshering then it was too wet when you began.
As for true dry-aging, most restaurants and high end butchers do it for 14-28 days, although some high-end restaurants will age some of their beef as long as 40 days. However, that is under rigidly controlled conditions and the meat is inspected daily. Also, long aging is generally done with primal or sub-primal cuts, rather than individual roasts.
Steaks cannot be dry-aged, the surface area to mass ratio is far too high. Roasts or larger pieces are aged, then trimmed and the steak is cut from the trimmed roast.
