I find it amusing that everyone rails against IE (rightfully so in many ways) for not following standards, but every web developer I know (and being one in a lively local web development community, I am exposed to a fair number) still has to check sites in IE plus a multitude of other browsers . When there are differences between standards compliant browsers, theres something wrong with the standard imho.
It's not necessarily a problem with the standard, it's a problem of specifications generally. Writing a specification that covers everything is very hard, and writing code to match a specification exactly is also very hard. You can realistically only get approximations. The same thing occurs with other standards. Look at how many differences you have between C compilers, Unixes, or (God help us) SQL databases – sometimes even when the standard is very clear.