The way I saw it, In Tim Cook’s presentation, the Apple Watch was shown to be an excellent Activity/Life monitor, where movement, lifestyle, and general health were emphasized, and not heart rate training. I could be wrong, but I think Apple knows heart rate is not going to be super accurate during exercise with the Apple Watch, therefore they built the Watch around making a great interface for activity monitoring - IE: how often you stand up throughout the day, pedometer information, etc. This will surely play out to be a thorn in the side of FitBit and other activity monitors, but I don’t think it poses a threat to serious heart rate training athletes.
I think Apple knows their job is to centralize the data collected from accurate sensors, not to necessarily create the sensor itself - except for activity monitoring. For example, Health Kit will allow all connected apps to push data that has been collected from different sensors directly into Apple’s Health App. I don’t see Apple getting into the Blood Pressure monitor or blood glucose monitor business any time soon, but apps that monitor blood pressure and blood glucose can push their data to Apple Health. I DO like the way the Apple Health App will centralize that information into one health app, along with other health related metrics. It makes sense to have all that data in one centralized location. The bottom line is that you should be able to use other heart rate sensors to do your workout and gather accurate data, you won’t be confined to only using the Apple Watch to collect accurate heart rate data.
Benefit of the Doubt.