They might have been trying to save you money, but in the long run it's always best to have rotors and pads replaced at the same time.
To explain more, cheep rotors are very common. What makes them cheaper? They are thinner and often softer, which means they wear faster and are easily warped. Resurfacing them is often a waste because the process of machining them can cause them to be even more susceptible to warping. Some mechanics are real pro's at it and others just throw it on and go have coffee.
As far as pads go, at best they need to be "sanded" to remove any glazing. Otherwise the pads won't grip as much and can also cause cracking which eventually will make the pad break apart. And again, if the mechanic is thorough they will take time to do this right, others may not.
As you can see this process is fraught with problems, even with a lifetime guarantee you still at least have to take time to go back and then sometimes pay the labor to boot.
So after saying all that, my advice is to always replace pads and rotors together and use good quality parts.
Take a minute to talk a parts shop with a good reputation, they'll give the skinny and what's cheap and what is good quality for a good price!