User blog comment:Zilla4444/AP Version of Black Cleaver/@comment-181.160.197.188-20120617021858/@comment-5009341-20120617104951

why more cdr? but less ap, it synergizes very well with rabadons and dfg, cause of the good ap,

while u can get cdr from dfg, athenes (u should get it on any ap with mana (not ryze though), cause it allows u to spam and u can pull ur combos more often off (during a team fight or laning phase) and with the 4% of masteries u will have 34% cdr,

if u then go for this item, u will have 39% cdr, if this item would give u more cdr, u would waste stats (4% cdr for nothing),

thats my reasoning behind the low 5% cdr