If you actually try to use Steal on a monster, you will realize pretty much you will get one item with highest drop rate, and because you can't repeatedly use Steal on the same monster, so I don't think it will be helpful to use Steal for more valuable drops. I personally used Steal to get hair for hair style changing, what I noticed was I hardly ever get second highest drop rate item from the monster when Steal was successful.
On the other hand, it probably just has a some sorta of formula that first reduce a fixed % of drop rate say ~0.1% then multiply with your Dex, then finally the skill level. What this do is to polarize the drop rate below and above 0.2%. For example:
Claw of Monkey 41% : 41+ (41-0.1 and some multiplier that is positively associated with DEX) = Its final value will be above 41% because highlighted portion is a positive value.
Tropical banana 0.040%: 0.04 + (0.04-0.1 and some multiplier that is positively associated with DEX) = Its final value will be below 0.04% because highlighted portion is a negative value.
I thought about it with statistic in mind, but it didn't help me because it did not explain the change in number of occurrence in individual item drops from Steal. Maybe someone can do better than my explanation.