More interested in finding why its happening (although I had a few good ideas) then actually see it happen I decided to try it out.

Using pricepes rather then hastati vs normal hoplites, with the default 5 ranks, its pretty easy to spot the main problem, the pricepes work arround the hoplites, so whilst from the front, they get slaughted, the real fun in on the sides, and ultimately thats where the losses come from.
http://www.users.on.net/~roehr/flanked.jpg

But apart from that, it seems as if most of the time, the 2nd and 3rd rows never get to fight with their spears! http://www.users.on.net/~roehr/rows.jpg. The circles show that the red and blue (3rd and 2nd) rows all pretty much line up, whilst the green (1st) row are doing tho fighting, so while we do have the potential of more then one spear attacking a target at the same time, the target doesnt seem to get close enough for the other rows to be in range. Thus the 'new' rank bonus is negated by tubby romans unable to pass between the first row of spears!

Of course, this same problem happens with the thin ranks. What really gives thin ranks more power is the fact that the AI isnt smart enough to attack the flank. http://www.users.on.net/~roehr/thinrow.JPG, so they end up trying to push though the ranks of spears infront of them, a virtual date with Death.