I believe you're wrong. This is how WhatsApp USED to work before they were acquired by Facebook. Remember how messages used to stay in the waiting (clock) state and you could delete them if the recipient wasn't online? Well now the first tick appears immediately because there's an intermediate server storing them for delivery and they can't be deleted from the client. It's similar to what Microsoft did to Skype.
I'm 100% sure that this wasn't the case. I'm not saying that there always was an intermediate server, but it definitely was before Facebook acquired them.
