Sleepycat's approach is to let anyone use the code freely with open-source applications, since they're giving something back by increasing the amount of open source code in the world. For those companies that aren't willing to contribute to the common good in that fashion, they sell them a fairly traditional software license instead.
This mailinglist is a way of discovering the meaning of the distinctions, in a series of well worded collaborative posts. From the paragraphs above it is possible to glean how the purists might object. Is theres something tainted in allowing closed software for a price? We will let you dump the oranges in the sea, as long as you pay some money to a charity? Or must these pragmatic arrangments be permitted until they become part of a more primary contradition, when Linux has world domination, and the battle is for the software that runs on it? I somehow prefer a clearer dividing line, but then what do I know, here in Windows XP!!