All browsers suffer from certain "characteristics" (a.k.a bugs) which are not necessarily 100% standards compliant.
When using CSS or even plain vanilla HTML it can be necessary to employ some pretty sophisticated hacks to cater to all browsers.
NetScape and Opera have far more problems than IE, but IE is certainly not perfect either.
The bottom line is that no browser is 100% standards compliant, although most of them claim to be to one extent or another.
Opera in particluar makes a big deal about being standards compliant yet it has suffered from some truly horrific issues and some users reverted to older versions for a while because a couple of versions ago things went horribly wrong. Many of these issues have now been ironed out, but many problems still remain.
There are no perfect browsers and one of the biggest complaints from any web designer these days is the fact that if you use pretty standard code, you can guarantee one thing: it won't display properly in all browsers without some serious tweaking.
IE, in general, is far more forgiving than anything else out there, but it does have its share of issues in interpreting code.