These are the 10 highest rated animes in AniDB as rated by AniDB users. An anime must have a minimum number of votes to be listed on the Top 10. You can get a longer list of the highest rated animes by going to the Animelist and doing a descending sort on the Rating column, direct link. This is maintained by the Routine Maintenance.
The Top 10 definitely will not be expanded to a longer list and may even be removed in the future. Having the Top 10 has led to a lot of voting fraud as people try to manipulate the entries in the list. Also for many people the Top 10 only reflects the most proliferated anime, not necessarily the best.