I have to chime in here.
There are some separate issues being blended here.
1) Distributors usually have an agreement with the manufacturer about dealing with warranty issues. Those agreements vary from no warranty at all to no questions asked replacement, and everything in between. In the end, the distributor is limited in dealing with warranty issues by factory parts and replacement support, or the set asides built in to the price. When the manufacturer will replace a defective product, if it's not in stock for immediate replacement by the distributor, they have to wait for the next shipment.
2) Manufacturers can't always dictate the level of spare parts and inventory the distributors carry. In some cases, the distributor or the manufacturer use an at arms length company to provide service.
3) How the manufacturer and distributor provide customer service and support is very often a make or break issue when making or extending an agreement.