They bring from R’ Elchonan Wasserman (Yismach Lev, Vol. 1, pg. 173 – Ohr Elchonan Vol. 1, pg. 268) as follows: We have to determine what the status of the aforementioned prohibition is, is it to do with stealing, namely, that since one has benefited from the meal, he should pay, and the way to do this is by making the chosan happy; or is it to do with the obligation to make the chosan happy, and one who benefits from the seudah, is obligated to make the chosan happy? The practical difference is, by an adam choshuv [important person] who ate and never made the chosan happy, by such a person there is no option that the problem is stealing, as the very fact that he came to the seudah is considered giving, like we find in Kiddushin (7a), if an adam choshuv accepts a present it’s as if he gave. If, however, the problem is that one who partakes of the meal is obligated to now make the chosan happy, then even an adam choshuv is obligated, and simply coming isn’t enough. R’ Elchonon says, the prohibition is the second option, therefore, Chazal say כל הנהנה – “Anyone who benefits” to include that even an adam choshuv is obligated to make the chosan happy.
