It didnt matter to me at all, someone implied that bethesda uses 'expansion' for big add-ons and 'dlc' for small add-ons, which is not true.
Also, it is not safe to say that they will do that. They didnt do that in fallout 3, their most recent game. Im not saying they do it exactly like they did it with fo3, though.
Half the size of SI is pretty disappointing after they said the dlc will be around the size of SI.
With All Due respect Bethesda has used the terms Expansions and DLC to mean large and small downloads respectively. In Oblivion none of the DLCs were big enough to be called expansion besides SI, and in fallout they increased the size of DLCs to be the size of what in Oblivion would have been an expansion. And lastly they went another step further and released an actual story continuation to FO3 9brotherhood of steel) that was an expansion.
Sorry if that doesnt seem to make much sense to sum it up I am fairly certain the DLCs are going to be in the same ballpark as Shivering Isles and when/if an expansion it will be likely larger than SI.