Nothing at all wrong with it. It's been a part of well established patent law for ages. Having it eliminates the need for an inventor to claim every theoretical possibility and keeps the patent office from being overwhelmed.
The memory manufactureres knew exactly what they were doing. They just thought they could do so and grind Rambus into the dust. That's not my personal opinion but a matter of fact. For more information on what actually transpired, I suggest that you read the 348 page Initial Decision by Chief administrative Law judge Steven McGuire of the Federal Trade Commission.
There's a lot wrong with it. Patents are supposed to cover your material innovations and reward your innovations with a limited monopoly. They are not supposed to reward your skill in expanding the text to cover the innovations of others. The latter is the direct opposite of the intent of the Constitution.
Luckily, some progress has been made to restrict that since the infamous Lemelson abuses of the system. He was able to patent bar codes after others invented them by tacking bar code technology onto his "machine vision" patents almost 20 years after the initial filing. As they say, "He didn't patent inventions, he invented patents."
They just thought they could do so and grind Rambus into the dust.
I know they were hoping to do that, but two wrongs don't make a right. I believe the overturning of Infineon's fraud victory was in error.