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Going responsive is the way to go if you ask me and most other SEO's out there. I'm not sure i fully understand your question though. Responsive design doesn't have any issues with Javascript in most cases. It would depend a lot on what the Javascript would try to do. As Andy has stated above Google can now read and execute AJAX and Javascript which is great. The only thing you should be careful is when implementing more Javascript is whether the website will still function as expected on devices/browsers that don't (fully) support Javascript. There are simple fallbacks and such so that all of your users get served great content and not just the ones with the most modern devices and browsers. Excellent book for more information on this is: Designing with Progressive Enhancement. Must read for any front-end web developer if you ask me.

That probably means they just have less html code, since it's a ratio (text/code). Text to code ratio has no impact on SEO, and I'm surprised some SEOs still obsess over it. If you have an incredibly code heavy page, Google may have trouble crawling it, but that's more about the sheer amount of code vs any kind of ratio. That being said, you should try to keep your html code to a minimum, as excess code will increase the file size of your page, leading to a longer load time which is a poor user experience and can have a negative impact on rankings.