The Difference Between A & B

Last week, I watched Mega Piranha and it got be wondering about the difference between A & B movies (or perhaps, better stated, the difference between a well-acted versus not-so-well-acted movie, since there are some REALLY stellar B-movies & some horribly stinky A-one). 

I know there’s the usual factors in a good versus a bad movie: better costumes, stronger plot, more money on special effects, but as I watched the Mega P., I began to wonder if part of the difference is this: w...