the fact the many browser are like an OS in the sense it's home for the web but many vendors tend to believe that they can control the web by shift their browser to standards to try to control it. Remember the web a free communication source that gave everyone in the world knowledge, where we all grow
How diferent browsers implement the language? How diferent sucky the communication with the DOM is? How verbose it is? How there are 4 ways to do anything and 3 of them are wrong and the one correct way has changed according to time?
I guess nothing.