Notice how everyone is mentioning really old guns? Practically everything mentioned in this thread are designs that date from the 1800s, and If you're willing to dig into the 1800s and early 1900s you can find pretty much every combination of features you could possibly think of. Keep in mind back then a lot of these features were patented and so new designs had to find novel ways of working around the patents used by pre-existing models.
Now, if you think of it from a modern production perspective, I feel like its a far better rule of thumb. All the patents with regards to revolver designs are long since expired, so any manufacturer can pick and choose whether they want a swing out cylinder or a loading gate. Once all those patents expired and gun makers settled on what works best things became more standardized - DA revolvers have a swing out cylinder, and the SA revolvers have a loading gate. I can't think of anything post WW2 that breaks this trend, although I wouldn't be surprised if someone came up with an example.