On this page, the two versions of this gyro/accelerometer IC have two different Logic Supply Voltages.
What is the VDD voltage?
Why would one version of the chip also have an option to make the voltage 1.8V?
http://invensense.com/mems/gyro/mpu6000.html
note: not intended to be a dupe of What is the difference between \$V_{CC}\$, \$V_{DD}\$, \$V_{EE}\$, \$V_{SS}\$.
\$V_{DD}\$ is the supply voltage (i.e. the main voltage "in" to power the IC).
Quote from 1st the link you posted:
VDD Supply voltage range of 2.375V–3.46V; VLOGIC (MPU-6050) at 1.8V±5% or VDD
As for why there's the 1.8V VLOGIC version? I suppose it's for those that want to interface with a 1.8V \$I^2C\$ bus (as opposed to, say, 3.3V SPI or \$I^2C\$ as you'd likely use with the non-1.8V version).
From the data sheet:
For power supply flexibility, the MPU-60X0 operates from VDD power supply voltage range of 2.375V-3.46V. Additionally, the MPU-6050 provides a VLOGIC reference pin (in addition to its analog supply pin: VDD), which sets the logic levels of its I2C interface. The VLOGIC voltage may be 1.8V±5% or VDD.
