Understanding the sensitivity of an L3G4200D gyroscope
@PeterJ is on the right track, but I doubt that it has anything to do with making the numbers "nice". More likely, the manufacturer wanted to make sure that the useful (linear) part of the analog sensor range always falls within the ADC range despite manufacturing tolerances. To that end, they gave themselves a 15% margin (7.5% at each end). This would agree with some of the other numbers in the datasheet, such as initial offset (DVoff) of +/-4% and a worst-case temperature offset (OffDr) of +/-2.4% at the extremes.

In other words, this sensor needs to be calibrated (zeroed) and temperature-compensated (for both offset and gain) in your application in order to achieve the best level of performance. The "extra" range of the digital output allows the sensor to express the full-scale rates in both directions without saturating, even when these errors all add up in the same direction.