Although they might have full text indexing and searching, databases and search engines/libraries work differently.
E.g. you come to online DVD shop and search for "Tom Criuse" (hint: misspelled surname). Every decent search engine (including Lucene library, not sure of others evaluated here) would yield a result, despite misspelling. I am not sure whether database fulltext thing would spit anything at all. It's simply built do do different job, that's it.