the webinterface is designed really for casual users, either those who can't be bothered to install proper irc software and want to start chatting straight away, or those behind firewalls who can't connect with a normal piece of software.
The webinterface is slow and bandwidth eating, both for you and for me. I can highly recomend anyone who uses it regularly to get a proper irc client (i do myself), but for a normal conversation the cost to me is negligable - it was only bought up in the past because of people running it 24/7, and only using it 1% of the time they were logged in.
I agree with the original post, by all means stay logged in for more than a couple of minutes, if there's no one around then leave it running in the background for 15 mins. It's the same way all real time communal things work online: chat, games etc, if people don't idle and wait then the chances of anything starting up is down to coincidence only