I've noticed on Amazon and on Walmart.com that there are 2 disc versions of all 4 Fast and Furious movies and some 1 disc versions also. I ordered from Walmart and from what I can see I got two 2-disc sets and two 1-disc sets. Are the 2-disc versions the same as the 1-disc set but with the added digital copy or are there more extras on the 2-disc sets? I am totally confused. Thanks.