There have been a couple of forum topics on this in the past. We’re really talking about several different things here.
One) first, the reason why in the past there haven’t been light switches that also had motion sensors in them is just because of the size of the Z wave radio. Since the new Z wave plus devices are smaller, we may start to see more. There is one Zigbee device which has been out for a while that could do this, but it’s kind of ugly.
- if you have a Lutron occupancy sensor (they may be the first people who use that term) it’s not a “dumb” device. It’s a very smart one. It’s just not zwave or Zigbee. Lutron is an engineering company which is dedicated themselves from the beginning to making the absolute fastest most reliable automated lighting, they hold a lot of patents. It’s hard to compare anything else to their devices. No one else puts that amount of energy into perfecting a light switch.
Three) in most cases, it’s actually better to have two separate devices, one that controls the switch, and one that is the motion sensor, because this allows you to put the motion sensor wherever it makes the most sense. Or even to use multiples for zone detection. Otherwise, and you see this in some office conference rooms, you get the situation where you have to stand up every 15 or 20 minutes just to keep the lights on. 
Some past discussions: