Why isn't there any higher bit DTS or DD tracks that an optical output can do 5.1

[Canada]

I was just wondering why there are not many disks that have a higher bit DTS track, that a DVD can't handle but still can be passed via optical cables. The only reason I am posting this is because I do not have an HDMI tuner. Which means I am S.O.L for a higher rate sound track than DD 5.1 if I decide that my Blu Ray player will be a PS3. Excuse me I can get better audio than that on quite a few SD DVD's that have a DTS tracks. Don't tell me it's a space issue either, alright on some Blu Ray's it maybe but I saw that Hellboy had 2 seperate PCM tracks an Engish and a German don't ask me why. If they have enough space on a disc for 2 PCM 5.1 tracks they should have room on some for a Blu Rays for a Higher Bit DTS or Dolby Digital track that can still be put out through an optical/Toslink cable.