Beyond that; the message is actually encrypted at the sender and only decrypted at the reciever. There is no record of the message being sent on Blackberry's servers. That's the nature of the system.
Also, BBM can also send attachements beyond pictures, such as Excel files, PDF's, etc. You can also do multi-person chats as well, something SMS and WhatsApp can't do.
Also pay attention to BBM Channels; it's like a mix of Instagram/Twitter on steroids. Currently in beta for Blackberry's only, but if this gets rolled out to other platforms, Blackberry could have a potential winner.