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Ditto for Common Lisp, where conditional compilation (with #+ and #- reader macros) is widely used to comment out s-expressions.

EDIT: I only now noticed it was mentioned in the article. I'll therefore add that the example from the article, of using #+nil, is actually not recommended, because it's technically possible that somebody adds a feature flag called "nil". Therefore, it's preferred to use #+(or) or #-(and) for comments (they're degenerate forms of conditional compilation expressions like #+(or flag1 flag2 flag3)).

It's commonly done in C with a #if 0 / #endif preprocessor macro.

D also supports nesting block comments with /+ +/, which helps when you have example code in your documentation

In what ways is that better than "if(false) { }"?

From linked examples it is clear that version() is allowed outside of functions. Since version() already serves a feature, there is no need to overload the meaning of if().