I think they specify what they have to sell at big markups in various markets. For example: Japan 10-30 for my Helix bought there, US 10-40.
Suzuki Burgman----US MA spec, for engine not sharing oil supply with trans.
Right now I use Shell Rotella 15-40 with MA spec.....but have 500,000 mile history since 1990 using WalMart house brand oil with no negative results in my bikes/scooters and 2 Miatas.
Strange---but Castrol (US made) available in Asia and Europe in militaryPX---will have label "for use in N America only."
What do shops (if you let them work on your bike) put in your engine? Usually what they have purchased in bulk cheap.
My take=clean, slippery, changed often just about anything works---as long as for 4 stroke engines. Not many people riding SilverWings actually ride them enough to wear them out.