I think the point was that the the OP was offered 50% "mile up" bonus and the wife was only offered 25%....
OP earns 4 miles per $ before the bonus. Wife earns 6 miles per $.
If wife makes the purchase, no 50% bonus.
I don't use the United shopping mall much anymore. Much better luck with Chase Ultimate Reward mall. Usually higher earning rates and the activity records and subsequent points post much quicker.
Transfers 1:1 into MileagePlus miles.