Good strategy, for a device to carry around ALL THE TIME
Yes, Sony did good to make it water-resistant. It is a good feature to have (unlike a bullet point, like eye following scrolling that only works in special circumstances).
Maybe not many of us will take a dip with our phones, but they do get laid on bar tables quite often. It is nice not to be bothered with the occasional beer spill (or a toddler's wet burp, as one commenter pointed out).
This version of Xperia may be preferable to some people, who found the the Z a bit unwieldy (due to the rectangular design and the size). And 720p resolution quite frankly is more than enough.
Me? I got the water-unresistant HTC One. And keep it in my trouser pocket at a bar (and quite frankly can hear it when it rings even there, if a band is not playing).