Meh, its not really a bandwidth limitation on modern Bluetooth devices, only that it negotiates a different Bluetooth profle. The high quality stereo audio mode (A2DP) has no support for microphones in the spec and is usually highly buffered, so it switches over to the headset profile (HSP). This mode is designed for compatibility all the way back to your old Motorola Razr flip phone, so it doesn't exactly have the highest quality audio options.

If we were to really look at it as a pure bandwidth concept, Bluetooth has plenty of bandwidth to handle high-quality, low-latency, compressed audio streams between two devices. There just isn't a profile written into the spec to handle it, so there's no standard way of negotiating that between a headset and a device.

https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles

>(A2DP) [...] is usually highly buffered, so it switches over to the headset profile (HSP).

Thanks for this information. That explains why it is reasonable to drop the audio quality.

Yup. It's really annoying to have to switch Skype back to use my internal mic every time, but not annoying enough to automate it.