The problem is, there are a number of different variables to consider here.
Black Cleaver is great if your target doesn't have too much armor. When I buy an item, I try to consider the % damage output it gives at that point in the game over not taking the item. The more armor my opponents have, the less effective the passive from BC is.
The thing about Inifinity Edge, the bonus crit damage is scaled. That's right, it always gives +50% base damage again regardless of what point in the game you are or what kind of armor your opponents have. If you have 50% critical chance (not hard to get), that's on the average +12.5% extra dps. Not too shabby on top of the +80 damage (which by the way gets counted towards the crit).
Finally, there are the numbers and there is what actually happens in-game. Most games I don't bother with crit because the chances are so low. In LoL, it's ridiculously easy to get over 50% critical chance. This means, at least every other hit is going to be a crit! With Inf. Edge, this means I'm doing 2.5X normal damage! During an actual game, you sometimes only get one more hit on a target and then your chance is gone. The chance you'll do a 2.5X spike and make the kill totally skews the game in favor of increasing a single blow. In my opinion, this gives crit % and + crit damage items something of an edge over increased attack speed items, or items like Black Cleaver that require that you get a few hits in before you start seeing benefit from the passive.
Just as a side note, it seems to be generally acknowledged that the two required items for a physical dps are Last Whisper and Infinity Edge.