According to Wikipedia:
Bluetooth v2.1 + EDR
Bluetooth Core Specification Version 2.1 + EDR was adopted by the Bluetooth SIG on 26 July 2007.
The headline feature of 2.1 is secure simple pairing (SSP): this improves the pairing experience for Bluetooth devices, while increasing the use and strength of security.
2.1 allows various other improvements, including "Extended inquiry response" (EIR), which provides more information during the inquiry procedure to allow better filtering of devices before connection; and sniff subrating, which reduces the power consumption in low-power mode.
So indeed that may be true. But this seems to concern only the standby mode. I'm a bit surprised there is such a battery life difference when you're actually listening to music.