If you look beneath the power switch there is what looks suspiciously like a rubber skirt around it - something that doesn't really need to exist on a phone unless it is to keep something in (for example, to stop light leaking from the screen backlight) or, more interestingly, to keep something out.
My guess is definitely with the latter. After all both Sony and Samsung have made advertising campaigns specifically boasting about the ability of their phones to survive an accidental or deliberate soaking. If Apple is going to compete then adding a degree of water ingress protection sounds like a worthy plan.
The only issues I have with this suggestion are that none of the leaked iPhone 6 chassis show any other form of ingress protection. You would certainly expect the volume buttons and home key / TouchID sensor to require protection if Apple were planning on letting you dunk your phone. The Lightning port, headphone socket and speaker could all be inherently waterproof by design, but those moving parts will require some form of stopper if Apple is looking to IP rate the phone.
So there are arguments and hints to suggest that Apple have, and haven't, made the iPhone more robust.
Fortunately there isn't a long wait until we find out one way or another.