The thing is, when it comes to balance patches certain events may have been designed with expectations of the balance units had at they time they came out. Also in many cases the balance changes are made not because the units were not balanced in the past, but rather due to the balance having shifted with new units that came out (ones we presently lack) that events need to take into account, thus having left some older units in need of a boost to stay useful (or become useful if it turns out they weren't strong enough before).