This web site makes the bold claim that most home bakers
cannot make a cake from scratch better than from a boxed
reasons are that the ingredients are better measured,and they use ingredients that you can't get.
He also says that making certain changes to the recipe
on the box results in even better cakes. He cites a
book, _The_Cake_Mix_Doctor_, which agrees with him and
describes some of these methods.
Most of his page describes the experiments he did to
verify the tips in that book, and to compare all of the
boxed cake mixes he could get his hands on. Most of
the tips didn't pan out, but the modifications he
developed worked very well.
I think this will come as a surprise to many bakers,
that making a cake from a box mix gives a better result
than most bakers can achieve from scratch with butter, etc.