Reading's policy is mostly to generate publicity.
In practice most universities outside the top 10 are taking grades lower than their published offers for the vast majority of subjects (leaving aside a few very-oversubscribed courses). Reading are simply admitting this upfront.
I don't think universities which are higher in the league tables will copythis, as they won't want to encourage students to be relaxed about dropping grades. In other words, while in practice even high ranked universities are taking 10% of students with one or more grade dropped, they don't want that percentage to be increased further - they want as many as possible coming in with the published grade offer.
Unconditionals and Reading's policy are primarily gimmicks to attract students, as is Bristol's contextual policy. (The latter gives lower offers to pupils from schools which are below average, many of which are not sufficiently low achieving to meet most universities' criteria for contextual offers.)
BTW I don't think Reading's policy is completely transparent, because in practice they are still going to have to take more than one grade dropped i.e. they haven't admitted what they will actually take in clearing.