Also many artists including U2 ship more albums to the stores then they can realistically sell which inflates the numbers a bit.
Retailers naturally order more albums than they can realistically sell in one week, which is why initial shipments are far ahead of initial sales figures. But over the weeks and months that follow, shipments generally come more in line with sales. Retailers don't order albums they don't feel they can sale, and the record company only ships albums to retailers that buy the albums. Then its up to the retailer to sell the album to the public.
In addition, soundscan which tracks sales at retail only tracks 95% of the market, plus back in the 1980s and 1990s, soundscan did not track sales from record clubs. So the shipment total more often in the long run is the true overall sales total. The stores and wear houses in the long run will only be holding on to a few thousand copies of each album in order to handle weekly or monthly sales after the album has dropped off the charts.
An interesting thing about singles today is that they only cost $1 dollar. I purchased my first single a 45 rpm in 1986. It was 3 dollars, about 1/3 the cost of buying the album. In todays dollars, 3 dollars from 1986 would be 6 dollars.
So singles back in the 1980s were 6 times more expensive than todays singles once you adjust for inflation. So single sales today are nothing really to brag about. You have to sell 10 singles to equal the sell of one album. So selling 7 million singles is like selling 700,000 albums. More importantly, if a fan will only spend 1 dollar on a single and went spend 10 dollars on an album, they are highly unlikely to spend 50 dollars or 100 dollars to see that artist in concert for 2 hours.
So as before, single sales represent light un-devoted interest. Its the album sales that represent true interest where the artist is able to build a fanbase and attract people to their concerts and to buy their merchandise.
As for One Direction, they are not even close to being able to match U2's record let alone gross a billion. There run of stadium shows is impressive, but as it currently stands, they will gross about $250 million, only about 1/3 of what U2 grossed on 360. They would need to play over 200 shows to beat 360 with the stadium configuration they are using and the ticket prices they are charging.