Netflix sends a steam based on what it detects as the maximum resolution it can send without video issues. you might have set it to the highest res, and netflix might say it's capabile of doing a higher res, but if your internet connection says otherwise, your doing to get far less.
Depending on your device, there might be a setup option that will actually test the network speed that Netflix is detecting, and that will give you far more insight to what is going on. On my Pioneer TV I can get it to let me know what the network streaming rate is. On most videos, it will start off lower and afer 20-30 seconds swap out to a higher res streem. The issues can be nothing to do with your insternet connection from your house to the ISP head-end, but outside the boarders of your ISP's network.
Axiom: ADA1000, LFR1100, VP180, QS8, EP500, M3, M3comp
AudioSource: Amp One/A