I'm convinced that companies like Autodesk and Adobe get *something* for recommending and even implying you need "pro" graphics cards, and I think it's one of the biggest myths in all of the 3D world.
I recently bought a GTX 460 with 2 GB of RAM: http://www.newegg.com/Product/Product.aspx?Item=N82E16814130611
And it works just great in Softimage 2012. Then again, my "old" GTX 285 was working great too, but it only had 1 GB of video RAM.
If it were only Softimage I was using I would have waited for the prices to come down a little until I could get a 500 series with 2 GB, but I needed something with more Vram right away since my Mudbox scenes are becoming more complex and RAM-hungry.
Now when you get into bigger and more complex scenes, the Quadros may begin to make a difference, when it comes to RAM, but when it comes to performance the difference is much less.
Of course, the official line is they can't support the myriad of gamer card varieties out there, and it's easier to test with and support the pro workstation cards, and there's probably a certain amount of truth to that, but at the same time they know that a whole lot of their customers are successfully using the GTX line and other gamer cards with their products.
For that matter, if they say they don't support your video card it's easier for them to deny you support if you have a video-related problem...
I also think Nvidia and their manufacturers are not being very smart about their pricing. They could sell those "pro" cards for half the price they are and probably sell twice as many or more and make up for it. I doubt it actually costs them any more to make a Quadro than it does a GTX, certainly not 4 times the cost. But that Quadro name on it is really all you're paying for.
Just my .02.