Ahhh. I see. That's a shame. Does anyone know if a altimeter would've added a lot of bulk to the watch had they added it ?
I don't think it is bulk, it is likely Apple does not want to add anything could suck up power. GPS, barometer, altimeter, are all power hungry, specially if left it on forgot to turn off, and AW is a smart watch with power hungry display and power hungry older mobile-phone like cpu, not JUST a fitness device, so it need to be able to take on more remaining action for the whole day.
I would prefer a fitbit-flex/jawbone-up2 like BT waterproof rubberized bracelet use it's own power for GPS, barometer, altimeter, activity tracking, & sleep tracking, and with it's own battery, and charge once a week, as BT side kick for AW.
I prefer bracelet than AW band with no display because there is always time we don't want to wear AW, but a waterproof rubberized bracelet will allow us to dive with it, play contact sport with it, surf with it, swim with it, sleep with it......all without AW for short moment, then it could BT sync with AW/iPhone when in BT range.
Apple might even be able to sell it as fitbit-flex/jawbone-up2 like fitness band also for iPhone, not AW replacement, but companion for AW or iPhone without display and without smart-phone grade cpu.