I think there is an overall feeling that Giant is one of the world-wide leaders in "quality" bikes and offer a bit more "bang for the buck". They actually manufacture bikes for other brands.
Before I get flamed, I'm not saying they are the best, or the only quality bikes. My point is they are ONE OF the quality brands.
I really loved the Defy Composite I tested. If I didn't want a Ti bike, that is the bike I would have bought.