As far as I undertand the max resolution brodcaseted on TV:
picture: 1080i (that is 1080 horisontal lines but only every second one shows at a time, thus called 'interlaced')
Sound: 5.1 encoded in a lossy compressed codec
Every broadcast system/channel has its own picture and sound quality/availability.
Bluray disc/player can play:
picture: 1080p (that is 1080 horisontal lines in every frame)
sound: 7.1 channels, 24bit/96khz (or is it 192?) in each channel (in several surround hd standards) i.e. lossless (?)
so, yes, there is an improvement availalble with blu ray for both picture and sound, subject to content actually containing it and hardware (bd player, av receiver, tv) being able to play it.