RP is great oil. Whoever is saying otherwise should have oil analysis done on their favorite oil, and then some done on RP after the same period. The difference is clear. RP's molecules resist shear and breakdown for a much longer period giving great lubrication and protection. This will be seen in the viscosity of the oil after so many months. As the molecules break down the oil gets thinner.
The whole "oil is oil" argument is from the uninformed. Sure, whatever crap you find on the shelves at autozone or whatever is all the same, but there are much higher quality oils out there. Just on the Impala I noted another 3MPG on the highway during my regular commutes just from the switch. I also noticed it took longer to warm up in the winter, despite having a new thermostat. Less friction, less heat, less loss, more MPG. People should have oil analysis done on their oil to see what is really going on. Anyone who thinks dark oil is bad and should be changed knows little about it.
The 3k mile interval was established a long time ago when we were using oils that lacked sophistication of even the crappiest of oils today. SAE certifications put modern oils worlds ahead of what brought around the 3k mile interval. An oil analysis done on even the cheapest of oils shows that most cars can run it for 6k before requiring a change. More expensive oils have better shear strength and will last even longer before breaking down. Something else key to look at for an oil though is its detergent properties. Synthetics have better detergents which fight and absorb acids created by the engine (rich conditions cause fuel to be mixed with the oil). If you never let your car warm up in the winter to evaporate fuels, it will turn to acid and overwhelm the detergents, so now you have some acid mixed with your oil. The detergents in the synthetics are that much better at offering your vehicle protection for extended intervals.
I change my oil twice a year, with some exceptions thrown in for higher mileage. I have an analysis performed each change to spot any early issues that could come up and see how I'm doing on my intervals. Each report says it can be left in longer, by up to 50% more than what I left it in for. I actually save money by using a better oil with fewer changes and my engine is better taken care of because of it. Plus, less used oil for the world to deal with. People who change their oil 3 months/ 3k miles blindly without knowing the condition of the oil are just pissing away money.
I'm not saying take my word on any of this. Do the research yourself. A few weeks before you'd normally change your oil, take a sample and have it analyzed. You will be surprised at how much longer you could go on that oil.
