[Sir_Substance]

Historically, those companies have held and mined with the current generation of ASICs (that their customers have paid for!), while they develop the next generation.

Once they have the next generation off the production line, they take the used previous generation, box them up and ship them off to their customers, and then plug the new generation into their mining pools.

If we could trust ASIC manufacturers to not sit on the best hardware, you might be right. However, for the moment everyone can get their hands on CPUs and GPUs of roughly the same power, while easily accessible ASICs are several orders of magnitude slower than the current state of the art.