Where the binomial distribution tells us the probability of getting a specific number of successes with replacement (i.e., equivalent with shuffling your deck, revealing the top card, noting whether its a land or not, then shuffling again and repeating), the hypergeometric distribution takes into account that card draws are, in fact, not independent (i.e., telling us the probability of getting a specific number of successes without replacement, where cards arent reinserted into the deck after being counted as a success or not)
My favorite thing about Archenemy, though
Two mana is obviously a fantastically low price for a permanent that remains on the board, constantly providing you with value until your opponent diverts attacks away to deal with it
Just be prepared, if you're looking to buy them, you could have to break open The Money Bin