In the case of the 1815 marching set I suppose they are meant to match HaT's French Line Fuseliers set which are not big figures.
I agree that there has been scale creep in the hobby with most of the manufacturers trying to put more detail on the figures and making the figures bigger to fit the detail in. These marching and command sets are, I think, a kind of retro-fit to add more marching and command figures to older sets that were made before the introduction of the MAC concept; so should they match the size of the older or the newer figures?
Perhaps the difference is greater with other fiigures but looking at the two on Chris's photo the size difference is not a big deal for me. The new figures eyes are about level with the other guys cheek bone and the body proportions are not way out of whack, I can live with it. Looking at a couple of figures that were sitting on the desk in front of me; the eyes of the Airfix highlander are level with the place where the Italeri riflemans' cross belts meet in the middle of his chest. That's a size difference (yes, I know one is 1/76 but I ain't convinced the other is 1/72).
There has been a lot of criticism about the 24 fig sets on the HaT forum: I think HaT has taken it on board and I suspect future infantry sets will be 48 figures. And, while there are still some sets being made with the old production methods (these ones included), with the newer sets made with digital masters HaT is going to some trouble to match the figures to the size their customers on the forum think is appropriate. That's a good development.