You're correct that it's very standard practice to add a 10% Service Charge to hotel bills in Asia. I have been told that this charge directly goes to top up wages to minimum wage levels. This practice caused a problem during the Great Plague when hotels were quite empty and there was therefore not enough Service Charge to pay foreign employees in Bangkok hotels the minimum legal wage for foreigners.

I rarely came across a hotel in Asia that didn't charge the 10%. Off the top of my head I remember the Four Points Sandakan (a hotel that sadly closed during the Great Plague) didn't charge it and I noticed this on the bill as an anomaly. I always assumed that such a Service Charge was charged everywhere but have never stayed in a Marriott hotel in the US to validate this. At least the Marriott booking engine allows you to tick a box on the reservation page and see all the rates including taxes and fees to easily compare.