Kyle,
IMO, you cannot separate the native cryptoassets from the app. You cannot implement the economics of Steemit using Bitcoin today, and the economics are crucial to the key value proposition of Steemit, which is near-zero barriers to entry for mainstream users.
The "Bitcoin argument" goes that eventually all these technologies will be available in an implementation which has the Bitcoin blockchain underneath. IMHO, this very well might be the case, but this argument ignores two basic facts of life from technology and startup world: (1) sometimes generalist platforms aren't the best solution, and you need specialist platforms; and (2) time to market and aggregating network effects matter (ask Facebook, Google, and Amazon and not Friendster, Excite, and Jet).
Steemit so far has demonstrated both concepts pretty clearly in practice, and even if it fails tomorrow on post quality, there is now a clear path forward for such a system.
There are other compelling reasons to want to have -- to use your term -- appcoins, such as, for example, disrupting the world of fundraising and private equity. We write quite extensively about that on the CoinFund blog.
Edit: For clarity.
RE: Hi, I'm Kyle. I've been a full-time Bitcoin writer for the past 2+ years. Now I'm trying out Steemit!