QEMU/kvm does this as a default, because keeping a more generic CPU / etc makes moving VMs between machines with different hardware possible. If you try to move a VM it won't work, of course, if the new machine doesn't support what the old did.
Not sure of this is why Apple does it. With KVM, you tend to pick a baseline that all your machines support.
Not sure of this is why Apple does it. With KVM, you tend to pick a baseline that all your machines support.