If you lease is written on the back of a napkin, maybe, but most landlords use boilerplate leases, and every boilerplate lease has a sublet clause. It's one of the most important clauses in the lease; why bother with the rest of the terms if the lease simply delegates all authority to the renter?
A sublet clause, yes. Perhaps I misunderstood your original comment because it sounded like you were saying that landlords personally vet all subletters. My previous lease did not have such a clause.
What did your sublet clause say, if it didn't say you needed landlord approval for a subletter? Think about what a lease that doesn't require approval for subletters is really saying.
