You still need to get someones number to add them to WhatsApp I believe.
Other apps like WeChat or LINE are very popular in Asia and you don't need someones phone number. Only need their username or you can add a friend by scanning a generated barcode.
WeChat is probably way ahead of WhatsApp. In China, people use WeChat for everything, such as ordering food at restaurants and even paying for everything at stores, bars, restaurants etc. Don't think we have that with WhatsApp yet.