I didn't think the Stingers sounded tinny at all with the stock pipe, it just wasn't quite loud enough. I can't answer the question on the violators, I've never had them, but the difference between a straight through muffler and straight pipe is the mufflers are typically cylinders with perferations around the inside of them to help absorb some of the sound passed through them. I'm sure there is more to them then that, but when I look in mine, that's all I see.
Straight pipes are well, just that, they are just straight pipes with no mufflers or anything.