To be honest I'm not sure one way or the other if the US Army has a Designated Marksman in every infantry squad but the USMC does.
A "standard" USMC rifle squad consists of :
1 x Squad Leader (Sgt w/M16)
3 x Team Leaders (Cpl w/M16+M203)
3 x Automatic Riflemen (L/Cpl w/SAW)
6 x Riflemen (Pvt-L/Cpl w/M16 + AT4's or other support weapons)
1 x Attached SMAW or M240 team (2-3 men with appropriate weapons)
One or two of the "rifleman" will be a Designated Marksman with either an accurized M16 or M14.
Given this organization is it a "Rifle" Platoon since less then half its people are riflemen?
Ever since early WW II when the Germans came up with the idea of building a squad around a machinegun pretty much every nation in the world has followed suit.
So maybe we should rename ALL "Rifle" Squads to "LMG" Squads
Or maybe be sensable and just call them "Infantry" Squads