@ Snagglefoot: While it might seem like it from the outside, the US isn't one "coast to coast" emissions standard. Many state have felt it worth their while to apply more strict regulations to address local issues. The biggest divide here is between states that have adopted CARB (California Air Resources Board) emissions standards and those who just have the Federal ones. Marine regulations are equally tangled up.
Regarding marine engines, emissions regulations started in earnest at the Federal level here in around 1998, with a gradual ramp-down in emissions to 2006. Many of the "classic" 2-stroke engine designs could no longer meet the new emissions standards and were phased out. The US doesn't typically "ban" a certain technology (carburetor equipped 2-strokes in this case), but lowers the emission standards to a level where they aren't likely to be able to be certified any longer. I believe the next level kicked in around 2011 or 12 which meant any lingering old-school motors were gone.
This march cost one manufacturer (OMC, the makers of Evinrude and Johnson brand outboards) their solvency as they banked on Ficht direct injection in the mid to late 1990's and it was a commercial failure. The assets were purchased by BRP of Canada and they re-introduced the Evinrude brand.
There aren't any "carbies" 2-stroke outboards here save for questionable quality imports that are based on outdoor power equipment designs (read: China built weed whippers) that dance in just under the displacement where emissions regulations become more strict. This point was chosen to not disrupt all OPE. All current offerings from major outboard manufactures (Mercury, Evinrude, Honda, Yamaha, Tohatsu, Suzuki etc.) are either four stroke (some with carbs, some with EFI) or direct injected 2-strokes.
Having recently adjusted the idle mixture on three carbs on my 2005 Mercury 2-stroke, I won't miss them when they are gone. I nearly had to burn the clothes I was wearing at the time and my eyes were stinging from the fumes. Someone with a Honda 75 had their motor running next to me in the marina on the last fishing trip and the loudest thing was the tell-tale splashing in the water. He fired it up and left, no fiddling with the throttle, no begging it to keep running while it's cold, no smoke cloud.
Regarding the "low horsepower models", how low are you going? Most majors offer a 3HP or less here. Maybe it's something with the market in Australia?
Also: Most of the manufactures are buying their smaller engines (usually less than 10HP) from Tohatsu and re-branding them as their own. Maybe Tohatsu has such a dominant share that it doesn't make sense for them?
As far as I know, Evinrude is the only one offering 2-strokes throughout their range (15 HP and up), these are far from the old-school "carbies" though. They have state-of-the-art direct fuel injection with stratified charge and other trickery.