If you want to optimize for other people's productivity, that's fine. But that's not what's best for you.

Also, there is a simple solution to this problem -- a program that converts $foo into HTML and a program that converts HTML into $foo. pandoc is an example.

Which me? Me the business owner that hires both web designers and programmers? Me the team leader that needs to manage a heterogeneous group of people, each with a different skill-set? Me the one-man-shop (and programmer) who outsources the design work?

If I have both web designers and programmers on my team having them communicate can most certainly be my problem (or at the very least a problem I am gravely effected by).

If only you had hired people that could learn new skills.

You can say that about any new tech, but truth of the matter is that there are certain advantages to using well know & widely used tech.

I'm not talking about zen-coding or pandoc or any tool specifically, you can make the same argument for e.g. clojure vs java: as much as you'd like to use the shiny new tech, you must at least consider the fact that it's a hell of a lot easier to find x new programmers that can use java proficiently than even x/10 that can use clojure proficiently.

It doesn't mean it should be the overriding deciding factor, but the cost of retraining/learning should at least be taken into account when making that decision.