Well, just because something has HDMI 1.3 does not mean it will decode or bitstream Dolby TrueHD or DTS-HD or LPCM.
For example, my ATI Radeon HD 4850 video card is "capable" of all that "HD" like HDMI 1.3 & HD Audio. But by itself, it cannot decode or bitstream ANY HD AUDIO.
Besides, I think the only gain you have from HDMI 1.2 to 1.3 is the PICTURE potential, not the HD SOUND.