The difference is that restaurants sign up to offer their existing delivery services to customers through H&L and Menulog, who are merely the conduit through which orders are placed. It's still the restaurant making the deliveries, and they can choose to pull out at any time.
It's crazy how popular they've become; just about everybody I know uses Menulog and Eat Now to order food, and if your restaurant isn't on it, we'll probably never know about you.
Menulog et. al are just discovery and payment gateways for those restaurants, so that they can offer an online service where they wouldn't be able to on their own. The establishments still handle all delivery themselves.
It's crazy how popular they've become; just about everybody I know uses Menulog and Eat Now to order food, and if your restaurant isn't on it, we'll probably never know about you.