Bluetooth specifications are established by the Bluetooth Special Interest Group of which Philips is an associate member (www.bluetooth.org). Just like with computer software there are different versions of Bluetooth and also of some Bluetooth protocols. In the market you will mainly find:
Bluetooth Version 1.2: The major improvement over Version 1.1. is less interference with other radio frequencies. (Introduction of adaptive frequency hopping).
Bluetooth Version 2.0: Bluetooth Version 2.0 by itself does not bring major improvements, it is mostly advantageous if used with the extension of EDR (Enhanced Data Rate). (Often spelled as BT2.0 +EDR). If EDR is used this increases Bandwidth (about 3x over BT 1.2). For headsets this is only relevant because it can slightly improve battery life due to improved duty cycles.
Bluetooth Version 2.1 (+EDR): The most significant improvement in Version 2.1 over previous Bluetooth versions for headsets is the introduction of “Simple Pairing”. This allows compatible phones to pair the headset simply by confirming the headset name on the display without entering a pass key.
Bluetooth profiles are not strictly tied to Bluetooth versions, e.g. Bluetooth Version 1.2 (and upwards) supports A2DP, but not every Bluetooth 1.2 or Bluetooth 2.0 device supports A2DP. Every manufacturer will decide depending on the application and required compatibility which profiles to support.