The original xbox actually has quite a few custom firmwares available for it without needing a modchip, along with custom bios if you want to TSOP flash. (as easy as bridging a couple connections on the mobo and running some homebrew.PS3 and PSP have CFW.
Xbox (the old one) had some form of CFW (NDURE) and 360 could be JTAG/RHD modded.
Therefore, your argument is completely invalid.
In fact there were many exploits that involved transferring modified saves to certain games, kinda like some of the exploits we have on 3ds.