They ARE lighter, they are smaller in diameter to be able to stretch. The Focus ones are like 3/8 (probably 10 mm.) and look puny.
Early on Ford was advocating reusing TTY up to twice if you measured them for the degree of stretch, 'beyond this point do not reuse' and gave a spec number; then the marketing guys won out by saying 'why are you not selling the parts??? And get rid of the repair variable!'
I reuse normal bolts but pay careful attention to torque pullup, if they feel weak they get tossed. Other than that I have no trouble using 40 year old bolts, depending on how many times they've been used. The block threads will be as weak as the bolts, really more since the block iron not as hard.
Using TTY on everything just makes full engine rebuild that much more disheartening, you gotta spend all that money now for simple bolts. Now they use them on even same/similar metals like main caps to block, and connecting rods, bust a rod loose simply to check bearings and you're looking at new bolts, and since new rod bolts really require remachining the big end to make them right then the whole thing turns into a mess. Obvious someone here is trying to scare you into buying whole new engine or even better, car. The day of the throwaway engine is upon us.