The slight distortions on the dialogs, I mentioned several times here and which for reasons unknown, virtually no ones seems to care, are shared by at least the AC3 and DTS LDs and the Cinema DTS of Jurassic Park. Hence, slightly distorted dialogs or not, this is most probably how Jurassic Park was simply meant to sound back in 1993.
Still more than 23 years later, there seem to be still mysteries unsolved about Jurassic Park.
Regarding Jurassic Park showing up on eBay: patience! Got two copies of it myself at a surprisingly reasonable price (at least compared to highly collectables like “Fight Club”). 😉
I think you underestimate the love and respect people here have for Jurassic Park. Actually having a print with cinema DTS to synch it to says a lot about how we feel. Since the slightly distorted dialog is present in more than one format I would conclude that it was there because it is probably supposed to be there.