It's not required and in fact it's a good deal for you (if the apartment is good and landlord is good). Most likely he is not the owner, he has a contract (lease of one year) and he is subletting it. This is how it works; if you are living in an independent house on sharing basis, nobody here gives or bothers about agreement/receipts (both the parties - Landlord and Tenant). Independent houses usually ask for first and last month only with no lease at all.
Apartments usually come with 1 year lease (which means you still pay only first and last month, but there is a contract for 1 year, should you decide to leave before the completion of lease, you got to pay him/her rest of the amount). That's why it's a better option to look for apartment on sublet option. This guy is most likely in a lease and is subletting you.