I definitively don't think so.
I think that to damage seals you have to keep the phone in altered PH for something like 1000 hours.
That's the time that high PH takes to melt plastic (salt at 0.5%, chloride at 0.003%, sulphur at 0.05%, and other chemicals normally in water).
That's would not occur in the entire lifespan of the phone.. as long as we are not fishes, and the exposure to water will be very limited for all of us.
I think it is safe to play with the phone in all kind of water all the time you like... i would just recommend to rinse after use and add an additional film to the screen or at least, do not remove the shatterproof film, as long as salt or chloride may affect glass clarity with time and time, xpecially if you take the phone to the sea all the summer.
IPX Certifications are serious things. Pressure is another matter, 30 minutes in one meter, means at least 10 minutes till 10 meters.. but i would not recomment using this phone for deep immersion with oxygen tanks. That's what is meant to be water resistant instead than water proof.
What that guy describes is a "splash proof" phone, but family like iPhone4/5 and Galaxy S2/S3 are already splash proof..
Iphone 4S immersion test:
http://www.youtube.com/watch?v=JKoMw-pMhg0
Galaxy S3 vs IPhone water test:
http://www.youtube.com/watch?v=If8G3UxeV-8
but they are not responsive to full immersion (beside, full immersion test have been passed from some of that phones) but the Sony XZ is really far from them.
Xperia Z: Chocolate test
http://www.youtube.com/watch?v=CE79SD9xtRo