I've missed tons of sales because I had no idea they were happening. I dont always have time to browse what random stuff is on sale this week. Microsoft could make a killing off this very, V E R Y simple feature. You already have our email, allow us to sign up for sale alerts and watch the money roll in. Or set it up like steam and allow us to add stuff to a wishlist and get alerts when those are on sale.
But seriously, this is a super basic feature, why has this not been implemented years ago?