Why does everything about WebAssembly make such a big deal about it being AST based rather than a stack or register machine? Sure this is a meaningful technical difference but I don't see why it's really a "selling point".
Here are some arguments from the guys who did something like this before for Oberon: ftp://ftp.cis.upenn.edu/pub/cis700/public_html/papers/Franz97b.pdf
To summarize:
1. Much smaller representation, which will mean faster download times
2. More control-flow structure retained, which means less needs to be rebuilt by JIT-compilers.
3. As a corollary of #2, we get easier and more helpful 'decompiling' of code blobs
4. Another corollary of #2: easier analysis for safety properties
