As it is now Sellers aren't supposed to profit from P&H are they ?

That could be one of the reasons they want the free postage.

Some sellers have been charging excessive postage and the free postage would fix that "little" problem,(eBay's analogy would be to clobber the many because of the wrong actions of a few),X-(

They main problems will be if the seller works out the wrong postage or combined postage as they wont be able to lower the end price, X-(