merged curaisse and greaves would make animation easier, less clipping issues between the curaisse greaves, and lets the designers be more artistic.
i never used 2 different types of armour anyway, i always thought that looked pretty strange
http://theelderscrollsskyrim.com/skyrim-armor-system-revamped/ says they are doing this so they can make the chest/greaves armor more unique and that works together pretty well.
They also mentioned they were adding more armor.
*They also mention in the article that so they can render the armor more easily and that allows them more people on screen.