That's NOT the way it is. The ATF has yet to, and most likely won't, classify the .308 Winchester/7.62x51 NATO round as a pistol round, unlike their earlier decision to classify the 7.62x39 as a pistol round. The only reason they did so designate the latter as a pistol round was due to Olympic Arms and their pending debut of the OA-93 autoloading pistol chambered in 7.62x39. That led to the import ban on steel-core 7.62x39 ammo. They weren't really concerned about the single-shot Springfield SASS, Thompson/Center Contenders and Encores, Remington XP-100, Wichita Silhouette, and other single-shot handguns chambered in rifle cartridges. The laws that are on the books concerning AP ammo revolve or focus on handgun chamberings or rounds which there are handguns readily available, and the ATF has left alone those single-shot examples I listed above. The autoloading OA-93 got their panties in a wad, however. Some say it was just a matter of time, because AK-pattern pistols were next on the docket.
Nor was the ATF terribly concerned about the Magnum Research SSP-91/Lone Eagle rotary breech single-shot pistol, which came out right away chambered in .30-06 Springfield.
For the record, federal law does not prohibit one from buying bulk AP .308 caliber bullets (Wideners.com) and loading them into .30-06 Springfield, .308 Winchester, .30-30 Winchester, .300 Savage, .30 BR, .30 Herrett, .300 Whisper, .30 PPC, .300 Win Mag, .300 Remington Ultra Mag, and so forth, there just aren't that many pistols readily available and chambered for them, especially "evil" autoloading versions. Likewise, when you make those handloads, don't sell them. (Which you're not supposed to do anyway, unless you're a Type 6 FFL holder)
Interestingly enough, SS109 and M2 .30 AP ball have been specifically exempted from the list of "AP" ammo, so they can be imported and sold by dealers. Here's the ATF page on the matter:
http://www.atf.gov/firearms/legal/armor.htm