I know several folks who set their default country as something other than the one they actually reside in, or they hide where they live completely. There are a variety of reasons for that--privacy, RP, a stalker they're avoiding, whatever.

The address tied to the form of payment might also not be yours--I've got others I know who aren't the ones who actually buy the points for dw usage, and thus were you to go off of the one whose address is on the payment, the address will be incorrect. (You specifically say IP geolocation, which shouldn't be impacted by this? But it's early and I'm exhausted.)