I wondered about the same thing since in past I never had issue with warranty issue so I asked the Sony rep in store and he exactly told me the same thing but I guess phones because the very same reason you mentioned are an exception for the time being.
How do you like that Tablet S? I may wait for the second generation.
It actually runs smother than the XS even with a weaker CPU/GPU. The screen is very nice as well. No complaints at all.
I would wait for the next gen. It should be out soon with a Tegra 3 processor.
http://www.xperiablog.net/2012/03/19/sony-prepping-tegra-3-ics-tablet-successor-to-tablet-s/