The answer is simple : They don´t care about this! Any modifications , even if this include just a higher resistance for the original 33 kOhm Resistor exclude any warranty.
I don´t know what kind of warranty some firms like Zoomhash offer , who sell modifed Blades , but if there is any , it is restricted...
There are surely some Sellers that offer some better conditions but have in mind that the manufactor exclude any warranty only if you replace or remove the original fan, this was the same for the smaller usb gridseeds who don´t really need a fan in scrypt mode.