With the WhatsApp Business app and new service, small businesses can now communicate directly with their customers in countries such as the Indonesia, Italy, Mexico, the US and the UK ahead of a worldwide launch that will follow over the coming weeks
WhatsApp vs Facebook Messenger whatsapp business app
I assume that Facebook pursues a two-pronged strategy.
1) WhatsApp as a narrow solution for direct customer contact of small and medium-sized companies, which should replace the SMS or e-mail.
2) The Facebook Messenger as a response or Copy Cat to WeChat in China, so as a large platform, open to developers, apps and chatbots.