In the bestseller list for that month, DC claimed 18 of the top 25 spots. That's pretty impressive considering not too long along it was Marvel who claimed that many. Do I think it's going to last? No. Six months from now it'll probably go back to the way it was. But that shouldn't upset DC that much. They've made their money with this gimmick.
If you average it out, however, 5 million comics divided by 52 titles equals only 100,000 per title. While that sounds great that's not actually spectacular. Companies were routinely selling those numbers in the 1990's.
If you bought the comics hoping they'd be worth something... sorry. I'm guessing you'll be seeing these titles in the quarter bin a few years from now.