@Bas, as daSmirnov already mentioned muting /unmuting your rear audio jack when you plug in to front ports is handled by device, not by your OS.
Earlier your OS never realised what kind of audio play back system you have. And it played all audio through the default device you have out there. Now what I can imagine is you can decide which audio stream goes where.. In Vista you were able to see what audio
streams are out there, and choose the individual volume, if the legend continues in W7 we will have an option to choose which play back device will get a perticular stream. That is what Larry mentioned when he said "this bluetooth thing will not handle music"
pointing to a hands free kind of thing which is suitable for audio calls but not for music.