I'm pretty sure all they need to do is direct you to the warranty provider, which isn't the retailer but the warranty company ie warranty wise, warranty direct, Motor easy etc and to be fair they'd rather the customer go direct to them to resolve any issues first hand. Also alot of retailers don't have an onsite facility to repair vehicles, also the owner could be circa 8hrs round trip away, how is it feasible to go back or for them to broker the repair? Some retailers apply possibly their own warranty on the vehicle but most will use a third party, to which it's their responsibility to advise the customer and discuss any claims. Much like a bump in a vehicle, would you go back to the retailer?
If you have first hand experience whereby the above is incorrect, I'd like to hear it genuinely.