Bud uses a blend of hops (I am guessing Tettnang, Hallertauer and Saaz are the main ones). Since crops vary in alpha acid content and availability, they can change hops from crop to crop and there will be no difference in taste (since each hop contributes little to the bittering/flavor). If one crop has lower alpha acid, they may skew towards another hop to balance out the numbers. If one crop has prices rise due to lack of availability, they skew towards a cheaper hop to keep costs consistent. It is all about the numbers. Make all the numbers match.
As far as adjuncts: Bud is mainly rice, while Miller and Coors are mainly corn.