Added:
17. Can't be pressed out of battery during a struggle. (Credit to tlawlyer)
18. Revolvers typically telegraph incipient mechanical problems before they cause the gun to stop operating – cylinder timing, failure to carry up, cylinder binding ("cramps"), extractor rod loosening, etc., all these let you know they are starting to need repair or adjustment.
19. A dud round can be bypassed by a quick trigger pull, unlike on a pistol, where the slide has to be cycled by hand to chamber the next round.
20. Needs less copious and less frequent lubrication than a semi-auto; less susceptible to becoming "dried out" or to suffering congealed lube like a semi-auto that has been stored for a long period of time.
21. Most common revolver ammo caliber (e.g., .38 Special) is not listed as "military" and thus not restricted in sales (as is 9mm, .40, and .45) in certain areas, e.g., Mexico, Latin America, etc.