Op amps are used for a variety of purposes. The example you used to multiply a 1V supply to 10V seems to be a very specific scenario where you desire a fixed DC output. In reality, amplification often requires operation over a range of voltages - for example, amplifying 0-1V to 0-10V. In this situation you would require an amplifier rather than just using a specific PS value.
Even if you simply want to boost a fixed DC voltage, it is generally easier to incorporate an op amp to get the desired voltage than it is to modify the power supply. Especially if the circuit is going to require multiple voltage levels, it is easier to have a single power supply voltage and multiple op amp circuits.
Op amps are also useful due to their high input and low output impedance. See more here: What is input and output impedance of an opamp?