It probably is more common to find integral suppressors made using a standard length barrel. Both the dual-objectives are served by "porting" the barrel, drilling a series of holes into the bore, then surrounding the barrel with a shroud containing the (sound and pressure-reducing) baffle stack. So propellant gasses are tapped off from the barrel and redirected into the shroud, leaving less pressure contained behind the bullet, reducing its velocity at the muzzle. The OSS's High Standard HDM of WWII was made this way:
And the ported-barrel integral suppressor is still common. That's what HK's MP5SD uses. And some of the aftermarket integrally-suppressed barrels for the Ruger MKIV and Browning Buckmark pistols.
But Ruger didn't want a barrel any shorter than 16" in this application because that would have made it necessary for the buyer to buy two $200 NFA tax stamps, one for the "silencer" (the term used on the BATFE Form 4) and the second for the short-barreled rifle (SBR). And starting with a a 16" barrel and porting it to achieve the desired effect only would have driven up manufacturing costs.
BATF accepts any muzzle device as part of the length of the entire barrel provided it is attached by a method they consider "permanent." Probably the most commonly used "approved" method is pinning (like bradding) used in conjunction with silver-soldering. For instance you could take the barrel off your AR15 to any NFA gunsmith and have him trim it down to 15", then add a muzzle brake or flash suppressor/hider or quick-disconnect for a suppressor, literally any muzzle device, so long as it extends >1" past the end of the barrel's muzzle, then have it pinned and silver-soldered. So long as it's at least 16" from the breechface to the end of the muzzle device, it dodges the additional SBR tax, even though the barrel itself is <16".
So Ruger skirted the whole SBR issue (reducing the buyer's tax liability by $200 in the doing) by permanently attaching a shroud which extends 16.12" from the breechface. From the perspective of the law, it's still a 16" bbl regardless of whether there's a baffle stack inside, otherwise the baffles couldn't (by the letter of the law) be removable. Which they need to be because rimfire powder is foul-burning stuff, and all rimfire cans need to be dis-assemble-able so they can be cleaned from time to time. But you'd be perfectly legal to shoot it with the baffle stack removed, because the shroud remains in place.
And I stand corrected. The barrel in this rifle is actually 10.62" in length, not ten even.