Remember that the Third Imperium was nowhere to be seen in the LBBs, while the low berth rules were there to model part of the inspiration for the rule set - the Dumarest series by E.C. Tubb.
When they started publishing what would become the Third Imperium, GDW never changed the low berth rules, although they eventually tweaked or changed outright a number of others.
So, it was either a joint oversight, or they didn't feel it needed changing for the TI, or the assumption is that low berths are actually pretty safe in the TI but they didn't want to change a core rule.