Here's a video by Grey Cook called Squat Vs. Deadlift. I get plenty of questions regarding the differences and which is better.
Grey explains these differences in some geeky detail. He also talks about why the hexbar deadlift is used to squat your deadlfit. The hexbar, like the squat, places more load on the knees and and ankles. It's also safer than the barbell deadlift because it places less load on the lumbar spine. It has also been shown that peak force, speed, and power were higher with the hexbar than the barbell. I tend to program more hexbar because of the safety factor, but there are definite and other quality benefits to the straight bar as well.
If you get a few minutes, check it out.