It's more easy for U2 to sold huge with initial sales only, with 25 years behind them they have a big and solid database all around the world, what Coldplay have not really, many people love Coldplay music but still waiting to see if they love 2-3 singles of the new album to buy the CD. When U2 release an album, it's not the same, at least 65% of people already know if they will buy or not the album.
In consequence, U2 singles are not so able to give a huge boost at HTDAAB like Coldplay singles can at X&Y.
In most of that, U2 release his album at Christmas time, so they kept fabulous sales during 1 month.
With all those points, I think that X&Y will outsold with not many difficulties HTDAAB in next months.
But Coldplay can wait a long time before pass the 130 millions mark in the world... lol