Negligible: means very small eg. the probability of a rare event might be thought negligible and we need not consider it worthy of consideration.
Negligence: means a failure, usually an omission, to have a system in place to protect people.
In this case bitscalper would be negligent if he allowed usernames and passwords out.
If another site lets out usernames and passwords it is that site at fault.
Point taken, negligible vs negligence, however I still say having passwords leaked is not negligible for exactly the same reason I stated before - this kind of attitude to providing services surrounding bticoin is extremely unprofessional and it undermines bitcoin as a whole, not just the site itself. If your consider your password 'negligible' then I have no more argument to make, but I am fairly sure the majority of people do not consider the security of their passwords to be negligible.
And as for the section quoted in bold, I'm pretty sure bitscalper DID allow usernames and passwords out.
edit: and to address theymos' actions being negligible, I think that comparing 'the passwords being vulnerable but nobody knowing' vs 'the passwords being vulnerable and everybody knowing' is also hardly negligible. It is true that this gives bitscalper the opportunity to fix their broken site, but if they're 'away for ten days' then... really... I just don't feel there's any need to say any more. This is not negligible in any way whatosever from any party involved.