I'd say so, yes.
If you want to "sell" a website, then the site will have to do something that not been done before, or something that is an improvement over an existing system which would make it worth selling. This will require coding using those languages or even outsourcing it?
On the other hand, if your looking to sell websites by developing websites for other people, you could learn how to use wordpress and stick to that.
You wouldn't be considered a fantastic web developer though, and probably wouldn't be very successful in the long run...