Note that VS and DS are just firmware representations. Niether should change within the context of physical NVRAM/EEPROM.
However, the developers have seen cases where power corruption causes issues within EEPROM and may trigger a write (false logic level) when it is not intended.
HW write protect is enabled by default for this reason as the application has to toggle WP for a write to occur, potentially helping to avoid these types of anaolies.
Because serial flash (as opposed to EEPROM) leverages a much more involved process for writes, this is not an issue with serial flash.