Zip Backup to CD uses traditional password-based encryption and authentication, which is not a strong encryption.
The basic problem with improved encryption is that it conflicts with the zip file format. If you create an encrypted zip file with strong encryption you've got a file no other zip program can read except from the program which created the zip file.
If you use the traditional password-based encryption standard in other programs, which creates files that, can be read with different zip programs they all have the same weak encryption. If you use a zip program with strong encryption you have compatibility problems.
There are known issues with the different strong encryptions used in zip files, a paper making an analyses of the encryption used in WinZip can be found at: