I've followed similar rules but have found myself ill in Darjeeling and Istanbul. The dishes and silverware (if there are any) get washed in water, so there goes that theory.
I was so sick in India that I forgot that I had a super antibiotic (3 pills for $160) my Dr. insisted I take with me in case I needed it. Never used them. I suspect it was banana lassi from a crowded street stall. An overcrowded restaurant in Istanbul got me there. After a hellacious night, the Dr. came to my room and said "you had doner kabab on the street". I asked him if that was a question? He said, "No. You had doner kabab on the st." Correct.
Of course you're not looking for it and should do everything to avoid it, but It's part of travel and an acceptable risk if one has a passion to sample the world. Beats hanging with other tourists at a Hilton.
"In pursuit of joys untasted"
from Giuseppe Verdi's La Traviata