I would disagree with that a bit. Certainly there are some schools whose diplomas aren't worth the paper they're printed on as far as the potential earnings a graduate will realize in the job market.
But a degree from a business school in the top 25 is still a ticket to a very nice income. I'll use Vanderbilt as an example, since it's a school I'm familiar with. They are ranked somewhere between 15 and 20 in most years. Their b-school graduates average about $80K their first year and signing bonuses from $10k to $15k. That's hardly worthless, even though it's not a top 5 or 10 school.
There are also some second tier schools that can give someone a boost of $15k to $20k in annual income. That's a worthwhile investment.
Go figure.