I would call the shoes "hyped" than a gimmick. Roshes were cheap pair of casual shoes and it actually went on deep discount ($40 at Nordstrom Racks) and that is really how people got into it and it just snowballed from there. The shoe was hyped because it became harder and harder to find because people started snatching them up once it hit the shelves and with the retail of $70, people had no problem buying several pairs since it is a bargain in comparison to retro Jordans & Nike that starts at $150+. But now, Roshe are pretty common, you can walk into plenty of shoes stores and get them, hell Macys has plenty of pairs in FSR.
So yeah, I would say the is not a gimmick at all as it promised nothing that got people to buy the shoe.