Most of the work I do is in java and ruby web apps. I've seen a lot of Railscasts, about 1/4 of DAS, and none of Ruby Tapas. I try not to binge on DAS because I prefer watching them one at a time and fully applying them before moving on. I think my problem is how big the codebase that Rails is and where to start contributing. I see your point to more experience but I'm not sure that's the crux of the issue.
The reason I mention experience is because Ruby itself has a lot of convention that you only get really fluent with through repeated exposure. Just now I went and browsed to a random Active Record source file and had no trouble figuring out what was going on just looking at the source.
A year ago I would have been lost like you. But now I can take individual pieces of a big codebase and grok them without having to understand the rest of it. You only get that fluency through experience.