Short answer is no , no player can guarantee to play all Divx /xvid type files , this is mainly because of the many sources for these files and the way that these files get made.
Divx/xvid files are the "Vegetable Soup " of media , unless you personally know the "Chef" , you dont actually know what your getting.
There are so many variables that its impossible for any player to guarantee compatibility with any file that you might get.
90% compatibility would probably be the best you are going to get.
With most files , if it wont play on your particular player , there is usually a fairly quick way to re-encode or re-mux to get it to play , that is the best you can hope for.
For around the £70 mark , the WDTV is a good player.