There really is no "right" or "wrong", it just "is." It isn't Disney or
DVC adding these fees, it is a contractor who provides the services for a profit.
The convention hotels have contracted package services and business services to handle the convention shipping and receiving. It makes sense that all deliveries are routed to that receiving center. It really wouldn't be viable to have to 2 receiving areas, or to have a "part time" contracted busness center open only if there is a convention going on at the moment, but have Disney handle it the other times. Those contractors don't provide receiving services for free.
This really is pretty common for convention locations, especially now that more people are shipping any additional items rather than paying the airline fees.
As far as I know, the non-convention hotels do not charge for receiving, but they do charge for sending a package, even if it is prepaid with the shipper.
Edit: After reading a few other newer posts on the resorts board, it appears this is in effect for all resorts now, convention or non-convention. Someone was charged at the Grand Floridian. I guess guests simply started shipping too many items, and additional employees were required.
Still, it adds less than 50¢ to each bottle of water in a case of 24, so it should stil be cheaper than buying it in the parks or at the resort stores.
No doubt, as I said, the sheer number of shipped items has increased dramatically since the airlines implemented their luggage fees. Disney has likely had to hire additional personnel to handle those shipments.
Here would be my complaint about it...at DVC resorts that don't have contracted package services with IKON, wouldn't our dues be covering some of those employee costs? If so, there is a least a talking point to try to get a discounted receiving rate for DVC Members. Though, either way, I likely wouldn't have items delivered.