"That's because new, better information has been discovered. Do you think there should be NO speculation on these issues until there is 100% certainty?"
No. I understand that studying the bones of T.Rex allowed them to draw better conclusions about how it likely moved. But looking at bones and a few fossilized tracks can only tell you so much about how these critters lived - the popular dinosaur shows state as fact things that are almost purely speculation, giving fuel to the creationist's claims against the science.
That "speculation" is based on
lots of evidence, both in the fossil record and through the study of extent creatures. The fossil tracks and the structure of the skeleton can tell us how the critter moved, and even how fast. Comparisons with modern animals can tell us how massive it was. Skin imprints (not uncommon for dinosaurs) give us a clue as to what it actually looked like. Fossilized remains of newborns tells us how independent the animal was after hatching; and the occasional remains of a parent with a nest provide clues as to the gestational habits of the critter. The teeth can tell us if it was a carnivore, herbivore or omnivore. The ratio of elements in the fossilized bones can tell us if it lived in fresh water or salt water (for waterborne animals), and give a clue as to its diet. Gastroliths found with fossilized remains also give clues as to diet. Fossilized nesting sites and the jumbled remains of drowned animals clue us into their social structure.
In other words, very little of the stuff you see scientists commenting on with regards to extinct fauna are pure speculation. Most of it is drawn from careful study of thousands of little clues.