It's a big problem for me. I would punch all the friends that sent my phone number to a company that use the laws from California and USA and not the ones from Europe, much more restrictive with privacy data. But I don't want to lose my friends so I just blamed on them and I asked to Whatsapp Inc for removing my phone number from their databases.
Are you sure that the oficial whatsapp only sends the numbers? Maybe you analyzed the protocol and you know it, I am just curious. It also stores the conversations, sent files, and more data... That can be read in their privacy policy.