The community sizes here at the current time definitely allow for more user to user interaction. It’s much harder for your voice to get lost in an overwhelming sea of useless comments as it tends to in the larger Reddit subs.
I’m not a twitter user but my understanding is that any replies to a tweet also apply towards the limit. So scrolling a popular tweet with hundreds of replies could drain your entire tweet limit in a matter of minutes.
Web apps allow for greater cross system support since they can be utilized on any system that has a browser and access to the internet. Another benefit is that none of the code is hosted on your local system (except the client side which is served to you in the browser). Web apps don’t necessarily lose any functionality, it just depends on the goal of the application. Web apps still have server side (remote) applications that serve the web app to your browser and which can perform the lower level functionality on the host system.