Is Transmit Power Control technology implemented in iPads?
This is a Broadcom question, and not an Apple question.  However, I wanted to provide some basic info on how the "low power mode" of the WLAN chip and iOS.

Lowering the transmit power is handled by the wireless chip, not by Apple itself.  For example, in the iPhone5 it uses the Broadcom BCM5334 chip which is capable of low power consumption (40-50% less than the previous generation) and "dramatically reduced standby power by 3 orders of magnitude."

Looking at the specs of the BCM4334, we find that it has "Programmable dynamic power management"  Going into the details we find that it the BCM4334 WLAN power states are described as follows:


  
  Active mode — All WLAN blocks in the BCM4334 are powered up and fully functional with active carrier sensing and frame transmission
  and receiving. All required regulators are enabled and put in the most
  efficient mode based on the load current. Clock speeds are dynamically
  adjusted by the PMU sequencer.
  Doze mode — The radio, analog domains, and most of the linear regulators are powered down. The rest of the BCM4334 remains powered
  up in an IDLE state. All main clocks (PLL, crystal oscillator or TCXO)
  are shut down to reduce active power to the minimum. The 32.768 kHz
  LPO clock is available only for the PMU sequencer. This condition is
  necessary to allow the PMU sequencer to wake up the chip and
  transition to Active mode. In Doze mode, the primary power consumed is
  due to leakage current. 
  Deep-sleep mode — Most of the chip including both analog and digital domains and most of the regulators are powered off. Logic states in
  the digital core are saved and preserved into a retention memory in
  the always-ON domain before the digital core is powered off. Upon a
  wake-up event triggered by the PMU timers, an external interrupt or a
  host resume through the HSIC or SDIO bus, logic states in the digital
  core are restored to their pre-deep-sleep settings to avoid lengthy HW
  reinitialization.
  Power-down mode — The BCM4334 is effectively powered off by shutting down all internal regulators. The chip is brought out of this mode by
  external logic re-enabling the internal regulators.
  


The algorithm that is used to lower power consumption/output will be specific to Broadcom and unrelated to Apple.  iOS only puts the chip into power one of the power states; it doesn't manage the power states.

Now, for the main question...


  Is Transmit Power Control implemented in iPads?


If it uses this chip (iPad3), then YES.


  The BCM4334 also supports Transmit Power Control on the STA together
  with standard Bluetooth TPC to limit mutual interference and receiver
  desensitization. Preemption mechanisms are utilized to prevent AP
  transmissions from colliding with Bluetooth frames. Improved channel
  classification techniques have been implemented in Bluetooth for
  faster and more accurate detection and elimination of interferers
  (including non-WLAN 2.4 GHz interference).