How do you define a "Cluster Bomb" in a meaningful way so that it can be bombed? "Any weapon carrying more than one explosive submunition?" Or only certain ones?
No country is going to adopt the definition above. But if you break it down, how do you do it? "Those with Point-Detonating Fuzes"? Okay, but our DPICM uses Superquick. By failure rates? One of the reasons why the US military is moving away from extensive ICM-family usage is because the published failure rates were far from what they were getting on the field. By size? You gonna ban hand grenades?
Rules about what weapons are "legitimate" and which ones aren't are often arbitrary and rather silly. Still, some you can define fairly well -- like land mines -- others, like cluster munitions, are not.
Cluster Munitions are on their way out anyway. Militaries like the US are recognizing the dud rate causes serious problems for friendly troops, let alone civilians. The Israelis may use them in Lebanon, but it doesn't do their cause any good. Soon Cluster Munitions will be alongside Napalm in world usage, ban or no ban. Heck, napalm's been banned, but the US has a napalm-like bomb it uses in its inventory; it's just not employed as widely as before, because it's not as effective as once believed.
(Napalm first saw heavy use in Korea. American pilots thought it great because it struck fear in the hearts of the Chinese and North Koreans, who would run away, whereas with iron bombs, they would keep moving. Prisoner interviews revealed the opposite: they were running because they knew they had a chance to escape the lethal zone).