IE, especially IE6, has had problems with standards compatibility. Especially HTML 4 and CSS3 (cascading style sheets). That was mostly because those standards did no exist when IE6 came out.
Since many big corporations kept using IE6 because it worked and because it was expensive to update, most responsible web designers had to do extra work to test all their CSS designs with IE6 and to introduce work arounds. It was a lot of extra work and they all hated IE6 because of it. I was in that group. But, it had to be done.
IE 8, 9, 10 are much better about HTML4 and CSS3. Most big companies have finally upgraded to Win7 and newer versions of IE.
Most web designers now assume that IE 6 is gone and don't worry about it. Their server logs tell them what web browsers are hitting their sites.
The problem now is that hot shot web designers really want to use HTML 5 features to produce really cool web sites.
HTML5 is in draft and the features are changing.
In September 2012, the W3C proposed a plan[29] to release a stable HTML5 Recommendation by the end of 2014 and an HTML 5.1 specification Recommendation by the end of 2016.
It is hard to build a browser that fully supports a version of HTML 5 that is not yet fully defined.
It is harder for Microsoft because they are committed to also support the IE6 quirks so that existing web sites continue to work. The other major browsers care more about the future than about the past. They have an easier task.
None of the major browsers fully support the draft HTML5 standard.
The best are about 30% compliant with the new proposed standards.
Try IE 11, it will have more support. It was released yesterday for Win 7.