The important part is throttling is based on the total amount of computational resources involved in "mining". So, if a breathrough in quantum computing increases the power of a typical home PC by a factor of 1,000,000,000, this won't have any effect on the number of new bitcoins generated.Quote from gnode:
I believe the 2040 time estimate is based on what is currently attainable with modern hardware. By 2040, computers will be far more powerful.
My understanding is that it throttles to an asymptope of 0, not 0 itself.