Howdy,
The OEM's are requiring that the units leave the dealers with an approved cutting system attached to the saw and functioning. With the Stihl, the only cutting system they recognize as meeting requirements is of their own manufacture. With Husqvarna, they will recognize Oregon product as meeting the requirements also. So if you're wanting a Stihl, you would have to supply the dealer with a Stihl bar and chain. For Husqvarna, it would have to be Husqvarna, or Oregon branded.
If you're expecting the dealer to deduct the retail price of the bar and chain from the price of the powerhead, it's probably not going to happen. The most you could probably hope for is about half of the retail price for the bar and chain deducted from the price.
Then you'll have to ask yourself, do I want to pass on a half price bar and chain to get a price reduction on a powerhead?
This is just a general rule. Depending on your relationship with your local dealer, you might do better or worse.
Regards
Gregg