But does have a different function, albeit with some overlap. The muzzle brake on my G-3 (rebuilt to semi-auto) makes the thing really uncomfortable to shoot from a covered shooting position, and a covered shooting position is darn near mandatory in the San Antonio area, unless you want your brains fried if you spend much time on the range in the summer. A flash suppressor would not have the same effect. Of course you could take the thing off entirely, but then the gun would look "funny".
If the second amendment were really observed we'd not have to make do with semi-auto clones of the rifles we'd really like to have. The ones we have a right to have, even under the "Miller" decision of the Supreme Court, namely the same ones the military, and some police, have.