I doubt that this is true.
When I had an issue with my 770 I gave the Nokia repair agent the serial number over the phone and he told me it was out of warranty as it had originally been for sale in the US. (The 770 was part of the sell-off of old stock that had been shipped to Europe at rock bottom prices).

If Nokia's practices regarding warranties has not changed it would suggest to me that the warranty for the 810 won't be a worldwide one but the OP may wish to verify the situation with Nokia prior to purchase if the lack of warranty is going to be a deal-breaker or not.