Answer to your last question: YES! Many of are here on this forum because of dependency or addictions to opiate drugs. I was taking Percocets for 5-1/2 months before I finally got off of them.
I'm siding with Boxerlover on this one. 4 week is not much time after major surgery, but he should start thinking about tapering down to get off of it in the next few weeks. Most people don't start getting the false pain from taking opiates after 4 weeks. It usually takes much longer.
What dose is he taking? If he is taking more than the prescribed amount, maybe you should talk to him about sticking to the prescribed dose. Depending on the amount he is taking, he will have to taper down instead of just stopping. After 4 weeks he's just getting into that gray area where a person can become dependent on it, but usually it is a longer period of time of taking opiates. Although, some people can become addicted in as little as 2 weeks.
If he is in legitimate pain, then he should take something to reduce it. Not everyone handles pain the same way. The doctor should be asking why he's still having pain and should be looking for reasons why he is still in pain.