Password as it relates to various encryption schemes
If the password is salted and is long enough to begin with, then yes, using the same password should be fine. (Though a bit riskier than using different passwords --- say, if you have one password stolen by e.g. a keylogger)

The reason for the recommendation "don't reuse passwords" is that it's often hard (or sometimes impossible) to know if the underlying software is properly using salts.