Well since the warranty is additional to statutory rights then yeah they can have any terms.
However, if he has a problem with the device then in the first 6 months the onus is on the retailer to prove that the issue is not down to a defect in the product. After 6 months he would still go after the retailer but the onus would be on him to prove the defect is with the product and not due to misuse etc. In any case my first port of call would be the retailer and if it was a reputable one, it would sort it out.
I would add that I'm no lawyer ( should be obvious by now) and that the Op should not rely on this but seek independent legal advice pertinent to his unique situation.