Maybe 80-lb pulse oximeters exist somewhere, but I've never seen one. Most oximeters are self-contained devices which are designed to slip over your finger. The OP was right to be skeptical about patentability, he's asking the same question I wondered about when I saw the headline.
Reading the Masimo link: it sounds like the "innovative" or patentable part is that they figured out a better way to get rid of motion artifacts. (They published an article on their tech way back in 1996: https://pubmed.ncbi.nlm.nih.go...)
I would think that, for most Apple Watch use cases, motion artifacts don't really matter. (They matter more in a hospital setting, where you might be setting an alarm to go off whenever the saturation drops). Eliminating motion artifacts is a "gee I guess that's neat" feature, like saying your watch is resistant to 300 meters.
I know someone is going to say "But I want to measure my O2 sats during a workout!", so let me just ask-- *why* do you want to do this? Are you worried your O2 sat is going to be "too low"? (If it's too low, you won't need an Apple Watch to tell you). Are you aiming for a specific level of desaturation (the way you might aim for a specific elevation in pulse rate)? Why? What's the "target" level you are aiming for?
The main uses I see for oximeter-on-a-smartwatch are 1) figuring out if someone who is short of breath needs to go to the ER, 2) keeping an eye on Grandma, and 3) screening for sleep apnea. All three of these goals can be accomplished even if your oximeter has motion artifacts.