We could always do an "Ask PG" to clarify, but my understanding of what happened with ViaWeb is you had a group of smart young people innovating on a problem against bulky institutional competitors. When asked who had an offering even close to what they did they said no one. (You might even say they were the first YC modeled company!) Viewed this way I'd say the success was about the people, not the language; they simply used their tool of choice.

I don't know what's the "official" (or real) story on current Twitter architecture.