There are also other audio transformer uses, converting amplifier outputs to 100V line for PA systems is a common one (and of course the opposite, converting 100V line back to low impedance for the speaker).
In the past driver transformers were quite commonplace as well, which gave the advantage of seperating the output devices from the rest of the circuit - meaning less damage when the amplifier failed.
But mostly, since the advent of transistors, audio transformers have become fairly rare things - even microphone transformers are pretty uncommon, due to their high cost and fairly low performance. Apart from the isolation aspect (DI boxes etc.), a semiconductor input stage provides better quality for a balanced input.