I started building a desktop app last year, but realized that many features I'd come to expect from using reddit/HN (like spell-check, and familiar keyboard short-cuts) weren't there, and I'd have to re-implement each one to mimic the web experience. (Do native apps for mobile get these for free?)
Webapps have surreptitiously become my standard for app features.
On the Mac, you can enable continuous spell checking by calling -[NSTextField setContinuousSpellCheckingEnabled:YES]. On iOS, continuous spell checking is on by default.
If you want to put together really simple interactions, then a web page will get you off the ground fast. The problem is when you get to the details. Harder things become more difficult, or just impossible.
For example, I don't think there's any way to control a browser's spell checker, beyond turning it on and off for a given field. (Correct me if I'm wrong.)
In a native app, I have implemented functionality so the spell checker would ignore text with a certain pattern, but spell check the rest of the input.
Webapps have surreptitiously become my standard for app features.