The only major difference between the Web app and the native app is built-in calling. There's currently no calling in the Web version.

Hi Nick. What about it being a Web app prevents it from being able to provide built-in calling?

We aren't happy with the available web calling options, yet. The more traditional route, Flash, has obvious disadvantages. More recently, WebRTC has been used for calling, but it's still too immature for serious applications. Long term WebRTC is the technology we'll choose for web-enabled calling, but it needs wider adoption among browsers and proven rock-solid reliability and quality for us to trust our sales team (and yours) with it.