It seems very weird to put the word "experiences" in quotes. It makes it seem as if the writer is using it sarcastically, or is in some way disclaiming what they are writing. What in the world justifies the quotes, and why wouldn't an editor get rid of them?
I think it's explicitlydrawing the reader's attention to the fact that the author is using the term in a way other than it's common meaning. To be pedantic I think the quotes are unnecessary grandstanding, if you believe in the term then just use it, but whatever.
Why do you only ask about "large points"? If you implement 'most of CSS, except for minute details', then you haven't implemented CSS, and web developers suffer because they have to add UA-specific hacks for your implementation.
Unfortunately, MS considers IE a Windows component, so MS supports all versions of IE that was ever released on a version of Windows for the life of that Windows version, which is a minimum of ten years total for each version.