I think that the people at Kobo know what they are doing. Probably they will lose $100 000 or more with these huge discounts, but they could gain more effective advertisement compared to traditional online advertisement with a similar budget. If nothing else, forum threads are not filtered out by AdBlock.
Forums and social networks are a potential marketing channel and can increase the popularity of a company, as long as the company gives them something to talk about. See similar tactics employed by the Dutch Airlines
here.