Checks are carried out to see if the file already exsists on the server and if it does the file is renamed.
Placing files in the database is very bad for performance especially with access as it would only take 10, 1Mb size files and your database would be over 10Mb in size slowing down the entire forum. Extraction of the files from the database is also slower.
In the next version files and images will also be placed in a folder named after the user for easier tracking of who has uploaded what.
Also the avatar uploading in the next version will only be available once a user is registered, thuse adding more security as unregistered users will not be able to upload avatars.