They are withholding the stock for unreleased cards in order to make sure that the stock channel of current generation cards is drained before they release new cards. They may further delay the release of the new next-gen GPUs if all the current gen stock is not sold off. If anything, it'll decrease the price of the cards instead of increasing it. Selling off current cards is currently a priority for NVIDIA and the prices are expected to fall even more. And whenever the next-gen cards are actually released, a huge existing stockpile will make sure that the cards are sold at a reasonable price.
What you say makes sense, but there's a whole different angle to see this too.

They regularly sell their cards as stock is available for MSRP. This article is about next-generation cards, not current generation tech. They are making sure they don't run into the same nonsense they ran into here lately with the bitcoin mining. They wanted cards being sold to gamers at MSRP.

When some douchebag company jacks up the prices because of demand, Nvidia doesn't get more money from that, they get the headache of consumers complaining about it.