Professional graphics cards are a segment of the industry that can look strange to gamers and PC enthusiasts. From the outside, it appears that businesses are paying more for almost identical hardware when compared to their gaming counterparts from both NVIDIA and AMD. 
However, a lot goes into a professional-level graphics card that makes all the difference to the consumers they are targeting. From the addition of ECC memory to protect against data corruption, all the way to a completely different driver stack with specific optimizations for professional applications, theres a lot of work put into these particular products.
The professional graphics market has gotten particularly interesting in the last few years with the rise of the NVIDIA TITAN-level GPUs and "Frontier Edition" graphics cards from AMD. While lacking ECC memory, these new GPUs have brought over some of the application level optimizations, while providing a lower price for more hobbyist level consumers.
However, if youre a professional that depends on a graphics card for mission-critical work, these options are no replacement for the real thing.