Unfortunately, the HBO swords will use different designs. The show has its own armorers, who will do their own original designs on the weapons and armor as seen in the series.
As to why you might want to buy these... well, for the same reason you might want to buy a Valyrian resin of Ned that does not look like Sean Bean, or a Dark Sword mini of Jon Snow that does not look like Kit Harington. Do you want a keepsake of the books, or of the TV show? If the show goes forward, you will have your choice.
Also, in the specific case of these swords, I retained the right to license out high-quality steel replica swords, and that license is held by Valyrian Steel. HBO has the right to license inexpensive toy replica swords. So if you'd prefer something made of plastic that you can pick up at Wal-Mart, that may indeed be available at a later date... and will look just like the weapons in the series.
HBO also has exclusive rights to do lunchboxes, key rings, and bobblehead dolls, among other things. It was a VERY long and complicated negotiation.