The breakthrough was a number of years ago, with Bayesian filters (I can explain more if you're interested).
It's dependant on your email provider to update their spam detection system accordingly. Some still don't do it properly. Hotmail for instance has long been pretty bad at this stuff.
Gmail is current the best there is, because it takes into account email from everyone's accounts, so if enough people mark something as spam in their accounts, then when the same spam gets to your account, it's automatically marked as spam. Other large systems don't allow for this.