I would assume people are just now noticing this because you can right click on a tech in TA and see the cost.

This is not new.  I repeat: NOT NEW.

What you're seeing is tech inflation.  Your first x techs (where x is a number that I don't remember somewhere in between 15 and...30?) do not contribute to tech inflation (except maybe if they were weapons techs...it's been a while since this has concerned me, so please forgive me for being more than a little vague), but techs thereafter do.

In DL and DA, tech inflation capped at 170% or thereabouts, or 270%/2.7x of total (initial) cost.  A normal tech will increase inflation by 2 or 3 percentage points, whereas finishing out a "tree" (tree is in quotations because it applies when you reach the end of line tech, so for instance the second tech in aquatic world colonization counts for our purposes, even though it's not technically the end of any real tree) increases it by more...I think this was dependent on the length of the tree, but to be honest I don't remember.  In any case, I don't recall ever seeing a finished tree increase the inflation by more than about 10 percentage points (example: missile weapon tree).

I haven't checked TA 2.x to see if the inflation ceiling has changed or how exactly weapons/defenses techs influence it now, but weapons/defenses techs in TA 2.x are given an additional hidden 1.5x/+50% modifier to cost after all other things are accounted for.

My apologies for being a bit blunt, particularly if your question is primarily with regard to TA 2.x's changed values for weapons/defenses techs (which is really only a modifier).

This is something I would be interested in, too.

I recently bought GalCiv 2 EU, after I played only DL about a year ago.

For some reasn I never noticed this issue in DL, maybe it's more pronounced now, but to me it seems that it's best to research some "key techs" fast.

Planetary invasions, e.g. would be finished after about 19 turns early on, but that increases to about 50 pretty fast.

Probably explains why some opponents in my games sometimes don't have any military ships for the first couple of years, or why some seem to have a couple of very advanced techs (compared to me) early in the game.