I thought the same thing. However, it looks like this was cleared up in another thread. It seems as though you are expected to join Living Social at then end of the training. So, it's not really an "offer" after all.
"expected" doesn't necessarily mean "required". Unless one of the things they have participants sign when they agree to do the program lays out specific penalties for refusing the job offer or leaving before 18 months, they're not required to do anything. And if such a clause does exist, there absolutely should be a lower bound on the salary, benefits, etc. in that contract, so that they know they're not agreeing to work for minimum wage for 18 months.