Well, they say it's supposed to last ten years.. in many places that isn't considered a permanent structure. I know here in Massachusetts, it has to have a foundation and be expected to have a certain lifespan to be considered a permanent structure as relates to property laws. Especially considering there's no reinforcing bars or anything, that's impressive lifespan for a temporary building! The ribbing where the fabric is stitched forms the load bearing members of the structure.
I have no idea of the price of the things, but in many cases I am sure that it is a fraction of the cost of virtually any other form of construction. The one they show most often is something like 50 square meters... that's a pretty decent area, requiring framing and such with any other construction method. The thing is easier to assemble than a tent.. only takes one person.
I also look at the smaller one, and having grown up in the Midwest where tornadoes are a common thing... if you anchored that thing (and I mean really anchor it) it's rounded shape makes it an almost ideal tornado shelter. Heck, the ability to put up a feedbarn anywhere in a single day with one man... what's that worth to a farm?
I have one of the prefab steel backyard lawnmower and junk sheds, it's running down to the end of it's life- I understand it's over twenty years old. When I looked at what it costs to replace it, you are looking at a thousand dollars or more in many cases- and I know from a mechanic friend who has done it- don't do the "assemble it yourself" kits, ever. Even cheap sheds are five to seven hundred dollars, and even if you just set out to build one yourself out of lumber, you are looking at a few hundred for even the most rudimentary-- and a lot of labor and knowhow to do it if you want it to last a decade or two. If one of the smaller ones was say, five hunded dollars-- it would be a real contender in that market. I know I would think about it... and in the meantime, I take window screen and lay it across the rust holes and hit it with that spray rubber coating (or automotive undercoating spray), and it'll hold for several years.. I am up to three years on one such patch 
Another very interesting material I have a yen to play with is UV-cure polymers. In all honesty, I want to build a 3-d printer which utilizes this rather than extrusion.. I think managing a UV LED or laser diode is a lot easier than a feed mechanism and temperature controlled nozzles. Just pump the liquid polymer and expose (harden) it on very precise locations, the extra runs down and is refed into the supply. The media management becomes a simple pump, the "print head" an LED or laser diode. All that's left is a gantry.