Perhaps this is a stupid question. But I purchased my OnePlus One from my country local ebay like store so I didn't have to get an invite. So if people can buy OnePlus one from Amazon for example. Why would people still wait for an invite?
If you purchasing oversea, claiming waranty is a hassle anyway and if the seller can handle it for you I think it should be fine to buy from seller other than OnePlus themself. No? (I should mention the seller should be a trusted one).