Exchange tasks? Rich?
"Business users don't get Tasks support, despite very rich Task support in Exchange"
Very rich? Come off it. Exchange's Task support is about as rich as a second hand car dealer with a lot full of Volkswagens.
A dedicated task service like Remember The Milk, Wunderlist or Todoist could be described as rich. Exchange's Tasks are best described as "you'll get a priority field, and you'll bloody well like it".
OK, perhaps that's a bit of an exaggeration. But what do you actually get? Priority, Start Date, Due Date, Status and "% Complete". Because everyone here would be willing to be a tenner on ever having seen "% Complete" being used by a real-life user consistently...
You can assign tasks to someone, which is nice. And you can set a reminder or set a task to repeat. And that's your lot.
In task terms, that's pretty much the basics.
What are we missing?
No tagging. No assigning to projects (although you could use Outlook's woefully badly integrated Categorize feature, I suppose. If you're a masochist.) No location field, or goelocationary features. No time estimation. Minimal postpone features. No filtering of tasks by anything worth a damn except the date and priority. No daily digest delivered to your inbox. No subtasks or task hierarchy.
Oh, and as we're talking about clients here - no browser integration at all. No, OWA doesn't count - I mean bookmarklets and browser add-ons that make your task list usable from any web page. The closest Exchange gets is if you use OneNote - a rather heavy sledgehammer to crack this nut.
To be honest, I could say the same about the Exchange Calendar or other areas. Microsoft keep buying tools like Wunderlist and Sunrise, but if they attempt to bring them into a monolithic system like Exchange they're doomed to fail. They succeeded because they were focused on being excellent within their own domain, rather than merely another component in Outlook.
They need to be running as little web services on top of Exchange, that can be accessed by https with a simple API, and that can therefore concentrate on having a couple of good clients and a decent service. Let the Outlook team figure out how to ruin the experience in Outlook, but at least you'll still have a decent underlying service and standalone client that does the job well...