Actually the sun WILL rise in the east tomorrow. Unless something cosmically disastrous happens between now and the morning, but the odds of that are of course infinitesimally small. That is a fact, not a "prediction."
We don't even know who the starting quarterback for the Steelers is going to be in September. We haven't seen any of the rookies participate in training camp, let alone take a single preseason snap. No idea if certain members of the defense will even decide to play or how they'll look if they do. No idea if certain free agent additions will perform more like James Farrior or Joe Schobert. No idea of how the offensive line will play as a unit, with at least two new starters.
So predicting the team to win more than two thirds of their games at this point is indeed a guess, but not a very educated one.