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Marc S.I don't think that many of the "top" current collectors have pedigreed slabs. It is mainly done for the purposes of selling -- and, as much evidence points to, it generally works. (with an exception noted to Mr. X)
That said, many of the current top collectors may not even have many of their cards slabbed. Keith Olbermann, who has one of the most extensive 19th century collection, has very, very few cards in slabs. There may be some exceptions to that, such as his Doyle card.
Others, like Larry Fritsch (RIP), it's unclear what may happen to his collection, but he definitely had two Lindstrom cards at one point, as well as rumoured to have multiple Doyle cards.
There are others I know of that have very extensive and comprehensive collections that are (generally) not in slabs, nor do they plan to be in the forseeable future.
Marc