Maths major here. I understand the concepts at work in regards to removing grain. Some detail is lost when grain is removed… it’s just whether or not it’s something that can be perceived by the human visual system. Removing most of the grain is a very common practice in post houses when it comes to grading film footage; as long as it’s done correctly and the grain is reinserted after grading is completed, the viewer won’t notice a reduction of detail. This is all beside the fact that what we perceive to be detail is contingent on many factors beyond the presence of actual detail.

Anyway, as mentioned, according to what I see on caps-a-holic, most of the blu-ray shots aren’t lacking in detail insomuch as they are lacking in grain and contrast; in the shot where Indy is holding an anachronistic rocket launcher, you can easily discern a detail as fine as the fringes of the flags in both transfers. Also notice that, in the HDTV cap, the flags have a very harsh border in the form of a black outline.

Also worth considering that the limited bit-rate of the HDTV capture will result in loss of detail to a further extent than the Blu (especially if some of those bits have to go to representing the grain).