How big is the problem of interoperability really? I'm the people guy in my company, not the computer guy - but I do a bit of programming for the web in my fre

How big is the problem of interoperability really? I'm the people guy in my company, not the computer guy - but I do a bit of programming for the web in my freetime in order to keep up and being able to deal with programmers on their own turf, so this question is out of curiosity - not trolling. In my sparetime I often do small sites that include javascript and CSS, which seem to be at the heart of the problem, and I have found that once you know a few hacks it is pretty easy to work around. If I can do this, then surely programmers will be able to as well. So my question is: Am i missing something? Why is everyone talking about the huge amounts of work involved in interoperability between browsers? Isn't it just a question of a few simple hacks in your css and javascript? Or am I missing something?