HTML (or XML or Lua or any structured programming language) is not a good fit for Darwinbots. At the most basic level, the DNA language needs to be able to both be programmable by people and by "closed" under mutations. By which I mean the mutations need to keep the program syntactically valid. Which you could still do with more structured languages but it means your mutation code has to understand the structure of your language, which injects some artificiality in to the system. Which undermines to some degree the "natural" aspect of natural selection.
The DB2 language and Sunweaver (the DB3 language) are designed such that any permutation of a valid program is still a valid program. Which means the mutation code can do the same sorts of mutations that natural DNA does, like transpositions and duplication and insertion, etc., without any special knowledge of how the DNA or program is supposed to be structured.
Now, all that said that's not to say human programmers need to program in that language natively. There's
PyBot for DB2, for instance. But the language is the way it is not by chance but by design. Compare against
Forth and you'll see many similar ideas, for instance, as an example of a sort of convergent evolution.