Like @dsa said... well kind of. From what I have witnessed, the 3DS and DSi (if using the Advance connection... pretty much required these days) allow for modern WiFi connecting technologies. The B/W series cartridges were setup with a WiFi connection manager that is limited to the capabilities of the the DS phat/lite. As a result, the system is actually interrupting that connection manager (in a manner similar to using codes off of the Action Replay.) At least from what I have experienced the Action Replay, unintentionally makes it impossible for the cartridge to communicate with the system properly for accessing the Advance WiFi functionality. I noticed an error changes between trying to go into the WiFi settings of the game with and without the Action Replay connected.
There is likely also some kind of firewall in place to help prevent online cheating cause versus one game freezing from bad codes the result would be the server crashing impacting millions of players. So, most players were already aware of this... as a matter of fact, there is a thread some where on here about not supporting cheating.
I think the real lesson here is remove the f***'in hardcase from your DS.