Program to Web Browser compatibility ?

From my understanding, it is just normal. IE, Firefox, Chrome and other browsers are developed by individual companies and so it is more like up to them to decide how to implement certain features. Sometimes, it is they decide not to implement some features (due to resources concern). Other times, it is just bugs (yes, every software has bugs and IE nor Firefox nor Chrome can be an exception). These bugs will then affect how the we page is rendered. So, why some websites work so well in IE but not others? Because these websites are developed by some others who may not have the resources to make sure they don't fall in traps into every browsers available in the market. Thus, when they are developing targeting IE, they may have to use code that are proprietary to IE only which surely won't be found in other browsers.

The main reason why some websites don't work on browsers other that IE is ActiveX controls. If some websites use ActiveX controls then they won't work on other browsers since no other browser supports them. However the number of such sites is diminishing and most sites are becoming more and more standards-complaint. Some sites appear different on IE because they are specifically designed for IE with some features which are present in IE only. Another reason could be that the site checks for IE and doesn't allow other browsers to be used for policy reasons etc.