Lol....exactly! ;)
well in a way the logic is simple.
Basically the top brass said, sure we will give you more power. But you gotta pay for it.
It is also a business theme. The cost to produce a IS350 is probably very close to the cost of producing an is250. After all, the work flow is the same you just drop a different engine into it. You still gotta pay the worker to drop one in there. But the IS350 can be sold for 4-5 grands more.
It's not the cost of dropping the engine into the car, the 350 is different and more advanced than the 250 in many ways.
Besides, historically we've always paid more for the bigger engine option on most every car.