The reason TTS was re-recorder is that the original recordings were at a lower bitrate that wouldn't blend well with the newer, higher sampler rates of TTS's audio. Also, according to one of the VAs (I can't remember who), the MGS1 voice quality was so unacceptable that Konami could pick up background noises of (ready for this?) TRUCKS ON THE STREET!
I wish I could quote that but that's what I remembered from various interviews and podcasts. Hope that clears the mystery!
Good info, I never knew that about the trucks lol. I think it was Ryan Payton brought that information out, thank god he's gone.