Neither the Apple website, nor the back of the watch, say "plated"... which is a legal requirement if it is.
I re-read the information and from the way it sounds, the case is made from 18K gold which may make this a very expensive watch.
What I don't know is what is the life expectancy of usefulness.
First off, most iPhones have had about a 4 year useful lifespan from the day they are released up until they can't run the latest OS. It doesn't mean they still can't be used, but if we judge the lifespan of an iPhone in terms of running the last OS, that's about 4 years. Add another couple of years until the thing dies completely and they can't be fixed or replaced with the exact same phone, but there were people still using 3GS's even recently.
Now, these watches aren't a phone, they are basically a Bluetooth device that runs a version of OS that's not iOS, but basically a trimmed down version of iOS, but I think this watch, providing the battery gets replaced, could potentially last a VERY long time since it just gets paired to an iPhone for taking/making calls and uploading fitness/health data. How long can Apple support these devices? Who knows. Maybe forever. Some of these older watches get so expensive to repair that it ends up costing more to repair them, then the watch is worth.
I can see Apple eventually offering other watches with more features, but that won't make these unusable, it will just make them not have all of the features of a newer design. But it may take a while until they can make newer sensors for more functionality. But at least they use high grade sensors and other components/materials which should make these things have a pretty long useful lifespan.
