The LANL archive has an advantage from the point of view of data management in that while updates of preprints are permitted, the old copies are preserved on line, and all copies are date stamped. Journals Journals display the final form of a scholarly work, and form an important filtering mechanism for the reviewing system. It is the journal version of an article that will be referenced, if possible, and that will receive links from Zentralblatt and Math Reviews . They should also provide the most stable links to the article. Thus, it is important to be able to conduct data searches restricted to journals alone.
Journals also are potentially much more complex from a data standpoint than preprint archives.
First, Journals can archive the same kind of supporting materials, interactive web programs, etc., that authors can place in their own personal web sites, as well as commentary by other mathematicians. The New York Journal of Mathematics and the Electronic Journal of Combinatorics are already starting to do this. Second, most journals will not distribute TeX source, and will only distribute graphical formats such as pdf, dvi, etc. Indexing pdf files is apparently possible, but would be cumbersome, due to the size of the files, even if it were otherwise efficient. I do not know of a way to index postscript or dvi files.