Silly, rollers don't teach you how to corner. They teach you how to be smooth. There's a difference.

Smooth is being able to ride while lightly grazing knuckles with another rider. It's about reacting to another rider's motion without overcompensating. It's about putting your wheels on a line and staying there while people are maneuvering around you. Smooth is all about the fine control enabling you to ride your bike to within the inch. That's what rollers teach you with regards to handling. Perhaps not as important for a recreational rider or a triathlete, but a vital skill in road racing.

And ararose, if you are finding it hard to go threshold on rollers, then I don't want to be anywhere near your wheel on a breakaway. That's another thing rollers teach you is how to be smooth when laying down the power. Even crosseyed, you still need to hold your line.

Also, rollers teach you nothing about acceleration. They can be used to drill on leg speed, yes, but generally you can't get enough resistance to do a lot of acceleration.