The idea behind identical VCOs is that, if you're doing some slight detuned doubling, you'll want the VCOs to behave exactly the same way in terms of CV tracking, nonlinearities, and the like so that the end result actually seems to sound like a single source. Technically, it's not 100% necessary to do this these days, but it does assure users that if they want a specific sound that requires matched VCOs (such as emulating Minimoog bass, and so on), it'll be easy enough to do without having to make an excessive number of tweaks to deal with dissimilar hardware.