It's not a straight headstock, but the angle is nowhere near the same as the angle on other RGs. *
The retainer bar is not attached to the top lock, it's just behind it. *The headstock on the USRGs is actually completely separate from the neck and is actually detachable. *I remember seeing an auction on eBay about a year ago where the idiot seller had actually locked the strings down at the nut and then removed the headstock permanently to "Steinbergerize" his guitar. *The joint where the headstock and neck meet is a brass plate and the string retainer bar is attached to that plate.
The USRGs are fine guitars, but the headstock angle and the proximity of the string retainer to the nut make tuning these things a pain in the a$$. *The reason is that you cannot lower the string retainer bar enough to make the strings sit flat in the nut before you lock them down. *As a result, when you lock the nut, everything goes way sharp. *To compensate, you have to screw down the fine tuners at the bridge and then back them off once everything is locked down.