Obviously having technical founders can have many benefits, including:
a.) Can create technical product yourself, spend less on coders initially (e.g. Zuckerburg)
b.) Some products may need complicated code even for a POC (whereas sites like Twitter, less so. Any mediocre dev could make a badly written Twitter clone)
c.) Easier to think of technical ideas. For example I doubt a non-technical person would think of creating BitCoin. On a smaller level, could fail to think of feature-sized ideas within a company.
I think that, if Twitter didn't exist and I decided to create it, lack of coding skill wouldn't be a problem, as long as I had funding for coders to replace the technical founder's early role. Don't get me wrong, I'm not claiming I could do what Twitter have done, but I don't think that the things I'd have done worse would be because of technical ability, the same as if I was hired as a lawyer my failings wouldn't be for tech/code reasons.
Edit:
As an example data point, the company I work for is a digital publishing company, creating and managing content websites. Founded by people from hardware distribution industry, and successful - yet I would argue that our core business type is similar to Reddit, in that success/failure comes more from business decisions than "wow, you coded a better website than other people!" (Reddit being better than Digg, for example, is much more than "Reddit is coded better".)