During the shabbos hagadol drasha this year (5774) our rav mentioned the statement that each of the arba kosos is regarded as a separate mitzva. He stated that many mitzvos must be performed 'al hakos'. Thus the cups themselves are not mi'd'oraisa, but the mitzva they are drunk for are torah prescribed. Other mitzvos that are required al hakos are bris milah, birchat hamazon, or kiddush hayom.
The four mitzvos in hagaddah are kiddush hayom, magid, birchat hamazon, and hallel.
Each mizvah has a bracha said al hakos for that mitzvah.
In the case of the question as asked it would appear that the answer would be "no", in one sense, and "yes" in another sense. That is, it is not the matter of the cups themselves that is from the torah, but the associated mitzva. Then again, perhaps the association may be what is being asked about (that is is the association of kos with the mitzva from the torah)