The £94 a week (essentially what someone would get from the JSA) applies to anyone coming in on a family based visa, fiancée or spouse. And it is after all fixed outgoings like rent, utilities, debt repayment, etc.
Also, it isn't entirely a magic number. There is a lot of discretion when it comes to family visas, and in a lot of cases they have to evaluate the situation when the immigrant arrives in the country and can consider things like job opportunties, potential of the immigrant to earn money, etc when looking at the situation.