Actually, is there a need to block anything? They're coming up with a mining-focused product line now. Just make them slightly cheaper per hash and voila - all miners will be buying the mining-focused products. They lack the video outputs so it makes sense, you can skip some of the BOM on the card, save a few bucks. As it has already been mentioned in the thread miners are super sensitive to squeezing every cent out of their setup. If they can save some bucks on cards, they will surely go for it.

So either the mining cards will be cheaper than regular, which makes this block a moot point in near future, or they will be more expensive per hash than normal graphic cards. In which case the block makes sense but in my opinion is a bad move by Nvidia. Making the mining cards more expensive than regular cards is throwing a gauntlet to the whole world to break the drivers or workaround the hardware. It will be fascinating to watch the cat-and-mouse game of hackers and Nvidia developers, but it will not fix the horrible GPU market situation we're in now and that is a shame.

Disclaimer: I want to buy a new GPU soon but for the MSRP and not the price equivalent of a small car. So I may be biased...