The article you listed is nearly 20 years old and was no longer relevant that same year it was written because Euro 3 emission standards came in 2006 for motorcycle. Motorcycles sold today have to emmit 5-6 times less CO than Euro 2 motorcycles that were modern when that article was written (not to mention other pollutants or bikes that were slightly old at the time, or 25 years old, as the article talks about, so bikes that are by now nearly half a century old).

I don't think any motorcycle sold in first world countries can legally not have a catalytic converter. Every scooter here in Europe has it.