Lemme just add my two cents in here. Standards are a good thing - unfortunately getting AOL and Microsoft to agree on a standard is difficult at best. Even with organizations such as the W3 standard committee making the standards these guys won't comply fully. So there are still a lot of things that will work on one browser and will either not work or even crash another.

If the developer has the time, he can do what is called Browser Sniffing. This is a small peice of Javascript code that asks your browser about itself. then the developer can code it appropriately.

Unfortunately this is a pain in the neck. So most of us just ignore it. There are ways around it, by using Java and the like (which will run the same on most platforms) but it goes back to the 80-20 rule.