Why is it always 10 cents cheaper?

Whether true or not, I've always heard that comapred to the major brands, it's poorer quality.

I have also always heard that it is lower quality, that it contained more alcohol than fuels from Chevron for example. I know for a fact that the one time I put in in my GX 470 I had some real issues with acceleration, I would floor the accelerator the revs would spike but I would get no power at all. My lexus dealer said they strongly discouraged the use of Arco gas.