Setting aside the connectivity issue (which is an occasional but serious one if you find yourself in Afghanistan from time to time, but I recognize I am part of a niche market), the browser itself is a general tool being bent toward a specific purpose, imperfectly.
The biggest issue that causes me to shy away is that I will occasionally do something to lose focus on the text, hit backspace, and watch horror as my browser goes “back,” flushing game progress. I know there are workarounds, but the player shouldn’t need to change default behavior to play; that itself can be a barrier if we are talking about new user accessibility.
I like being able to quickly change font sizes, colors, etc for better readability. These controls are rarely implemented in an easy-to-find manner in a browser; would they even affect the game?
I use Google Docs when I need to edit something away from my desk, but when I have access to a thick client, I prefer it. It’s more responsive, more fully-featured, and loads just as fast on no internet connection as it does with a good LAN (or a high-latency, low bandwidth link from a remote land).
Again, web access is great for outreach and occasional use, but if web-based interpreters were the only way to play, I probably would not have played long.
[Sorry for typos or lack of clarity; typing with week old baby in my lap.]
Sig