Your argument is similar. Everything you have on your machine right now works fine as it is. What you aren't taking into account is that the list of things on your machine is defined by the machine's limitations. A new style of computation will open doors and allow things onto your machine that are currently not possible because of limitations in your processor.
Ignoring that, I agree with your point wholeheartedly: just because things work now does not mean we can't optimize. In fact, a very large part of the software field is all about optimizing things that already exist.