Read, and think about, and if you agree, link to, Joe Clark’s article Compatibility of Weblogs and ISSN, which elucidates several reasons as to why Weblogs should be eligible for ISSN, and why currently, many are rejected out of hand. This very weblog was rejected, although I did apply for one within weeks of starting it, which may have contributed to it.
(Link lifted from, and linked to by request of Zeldman)