Whilst Loye did well in terms of attacking the opening bowlers, he failed to turn some decent starts into big scores, we need our top order batsmen to be able to convert these starts into 50's and 100's, I think with Joyce, Bell, Vaughan and Strauss all capable of opening the innings and proven they have the ability, technique and temprament to make big one day scores, the need for another opener was probably deemed inappropriate.
Bopara offers more options than Loye, he is another bowler and offers cover for the middle and lower middle order batting, if Vaughan fails to recover in time then Loye would be the obvious replacement. IMO the selectors have got it just right.