I always have IRC Client installed on my Linux systems, preferably with GUI but I sometimes install console one "by accident"
Windows is diffrent story, if I have clean Windows after formatting I can't manage my head to remember what should I install one by one so I just wait for moment I will shout "dang I need that one" and just install it (on Linux I have usually IRC Client installed by default so no drama...)

I vote for better ways to provide IRC possibility on web pages and I believe that Mibbit is good start to find out better ones as time passes, for example wsIRC You mentioned