Neolock,
Yes, if you jump through all the hoops, it IS legal. Hi-cap mags are imported all the time; in fact, that's the PRIMARY source of the hi-caps on the market, except for a few exclusively domestic guns (i.e., Rugers) and AR15s. That's why the anti's are trying to ban ALL importation of hi-cap mags.
M4,
Yes, we are ALL well aware that smuggling of many contraband items continues, and that DEA, Customs, Immigration, and even Miami Vice don't catch them all. If this were not the case, the amount of drugs in this country (for example) would be significantly diminished.
What's your point? That people could smuggle in mags? Sure. But mags are big, bulky, noisy, heavy, and not worth that much money, compared to, say, heroin or cocaine. Which is why it isn't done much.
-Troy