That is simple. Its because hikvision only provides warranty and support for cameras purchased from an authorized distributor. Doesnt mean the camera is any different. Sometimes the difference is 60, sometimes is 200 or 500 or 1000 depending on the cam. For someone installing 10 cams they can self insure....If you buy from reputable sellers they will replace it, as will paypal etc if they fail to.
As far as getting better image quality from hikvision sold locally that is bulls and you know it. It varies by the SENSOR in the camera. Compare apples to apples.
They are not "knockoffs" they are hikvision cameras made by hikvision. Understand that there are two types of china cameras, those that are made for the china market with hacked china firmware (not upgradeable) and subpar sensors and housings, and there are hikvision cameras that are made for the international market that are EXACTLY the same as the ones you buy from your local distributor, just cheaper.
The members on the this forum have been buying international dahua and hikvision cameras for YEARS much to the chagrin of distributors installers like yourself who want to justify the markup...nice try.