I am a newbie lesswronger, so it might be an already asked question, but I can't find an answer in the FAQs. I also don't have any idea of how many resources are needed to support a blog-app, given an already developed site/community. I would be glad if someone could explain the issues/difficulties, and why the community never exploited this channel to acquire new users/better accessibility (I would love to have an app instead of using the browser to browse the site).
I'm not part of the LessWrong developer team, but I am a software developer. Generally, a relatively complex app like this would at least require an developer or two working full time for a year, which would be a very significant up front investment, plus any new features would have to be developed for both platforms in the future. This is doubly true if you want both an iPhone and Android app and don't want to use one of the somewhat questionable cross-platform frameworks.
Given that the LW team is (presumably) budget constrained, this would mean that they wouldn't be able to work on anything new for the website during this time. In addition, the work would be completely different from designing the website, meaning that it might take extra time because the team would need to learn the relevant skills.
On top of all of those supply-side constraints, there's also the question of demand. I'm sure that the app would be useful for you and for others, but I simply doubt that there would be that many users. However, I do think that it would be a decent idea to poll active LWers and ask them about various potential future features, including an app, and if an app got significant support, then it might be worth prioritizing.