I take aroa's point in that purely from a safety perspective it should not matter if a flight is private or commercial - safe operation of an aircraft in theory should be clearly defined and applicable to any operation. Naturally things would scale with different operations and requirements, but the type of operation should not change the safety requirement.
That said, its been shown time and time again that when money gets involved, corners are cut and the fight between safety and making a buck comes down to the scruples of the operator. If common sense were common, you would not need regulation. History has shown that regulation is needed.
So in that case, where do you draw the line? If you say one operation because it is close to private, is small scale, maybe is not even the focus of the business should be excluded, what happens when a less scrupulous operator frames their operations around that loophole? When does it go from flying some cargo for a mate for a slab to a cheap freight operation with overstretched aircraft and pilots? And when that happens who is watching to ensure that the almighty dollar is not overriding common sense.
And in that respect I do think there needs to be a commercial aspect to safety regulation - by regulating commercial operations you have a framework and oversight to enforce safety standards. Maybe what is defined as "private commercial" needs some refining, but its a grey area and I think if you loosen it up you will have operations using those loopholes to push the boundaries.
Maybe dollars are the answer - an operation is private if it is a single person, not hired or hiring others and below a certain yearly income value. There should be something that gives scope for PPLs more certainty they are not in breach and maintains the spirit of a safety regulation. I don't think its a simple question to resolve though.
Just my 2c.