The bolts you are referring to are called a "caster/camber kit." From the factory, the R51 does not come with adjustable bolts on the front suspension, although it does have them on the rear suspension. To ask why not, you'll have to ask Nissan, but it probably comes down to them saving a couple dollars.
Installing the caster/camber kit in the front, which replaces the "regular" bolts that attach the lower control arms to the frame, allows the caster and camber to be adjusted at the front wheels if they are not withing specs. You can get aftermarket kits and they are relatively inexpensive, but they are not nearly as good as the ones from Nissan. The Nissan "kit" is not sold under a single part number, rather each part is sold individually. For those part numbers, refer to this thread:
http://www.thenissanpath.com/viewtopic.php?t=11989
Hopefully, the bolts will come out easily, but, sometimes the bolts will seize to the steel sleeve of the control arm bushing. If this happens, the bolts will need to be cut out using a Sawzall and the control arms will likely need to be replaced, which adds additional cost and labor.