It never made sense, given that the entity issuing the rebate isn't the same one you're paying. Like if your employer (or really, anyone else) cut you a $1M check because you bought a $1M house from a random person, is that really not taxable income because it was a "rebate"?
The real ruling is that as long as you're not doing obvious scams and scandals with tax avoidance, the IRS doesn't really care.
So if you're getting "the equivalent" of $1k a year untaxed, the IRS yawns.
If you figure out how to run your entire salary through airline points, the IRS wakes up.
(The laws are complicated to decipher, but they basically come down to the above. The tax courts will look at things like "is this available to everyone, how much was it, etc, etc".)
