I had the same problem for a long time. People would ask me to play a song, and I would just shrug my shoulders and say - "How about a scale?" Needless to say, they weren't too impressed.

People always want to hear something that they recognize. It doesn't matter if it's Happy Birthday. It's always necessary, at least for a serious guitarist, to know the theory behind his instrument. But people are gunna want to hear some songs now and then, so you should go ahead and learn some. My advice would be to continue with the theory and to learn a few simple songs on the side. You'll be surpised at how learning songs can improve your knowledge of the instrument.

If you play A minor pentatonic and start and end at C, then it's C major pentatonic.