Don't buy something before it's out. Simple as that. Stuff get's canceled/scrapped/blocked/etc all the time. What if gateway just closed up shop right now and didn't release anything else? Would you be happy with your purchases? I don't see why that's such a big problem for people. Gateway is a company which makes products for you to purchase. They aren't a public service, and they aren't obligated to release the stuff they show off. Go look at any number of scrapped games. You gonna complain since you can't get those either? If you bought a N3DS and it turns out there's no support for it, then that's your own damn fault. Not gateway's. Just like how if you updated to 9.4 it's not gateway's job to fix that. If they release a 9.4 exploit then great. If not, then no big deal.
They're not obligated to do anything, but you cannot deny the fact that it was shady business to post an advertisement video of the Gateway working on the New 3DS and then lead their customers on in a series of deceptive text posts claiming that the next release would include N3DS support.