You’ve told the story just as well, in 2 paragraphs!Lol.
On the gap with SaaS sites, it does exist, at least in China. The ‘official accounts’ of businesses and other entities within WeChat is built on HTML5 and CSS like any other websites. But because it is integrated with the WeChat app, users can subscribe to an official account and get notifications from the publisher whenever there is an update. In this fashion, you get real time notifications and other interactive functionalities like change your appointment with a neigbourhood doctor or order a bottle of milk from the grocer downstairs without having to install another app.