As with any area of business, things get diluted as time goes on.  You get one price comparison site, then there's a million and only the fittest survive.  You get one popular MP3 player and then you get a million clones and again, only the fittest survive.  You get a 3D content website such as this (one of the first) and then there's a million others and yet again, only the fittest survive.

Because of that, I'd say that any 3D content business packing up is doing so because they're not one of the fittest.  You either market and run your business successfully in a manner that is attractive enough to keep your business afloat, or you don't.  Businesses generally only close because they failed to achieve their goal, but that should never be taken as an indicator of the state of the industry it failed in.

I do believe that Game Engines such as Unreal are a direct threat to programs such as Poser though.  I was taking a good look at Unreal a few months back and it's mind-blowing what can be done, no need even to wait for a photoreal reneder, it's done in real time.  I reckon both DAZ and Smith Micro need to get those viewports replaced with a realtime render implementation as soon as possible.  Those game engines could suck-up their custom like a sponge if they don't!