There is no version Like BE 11 its just 11d and it have two version 11d 6235 and 11d 7170
The major chage in 11d 7170 was that it supported Exchange 2007 .
There is no major difference in the Backup exec build its just new enhancement are added to the product .The differences make sense as long as is functional to your environment
refer the following for BE 2010 ..Look in the whats new section
http://www.symantec.com/business/support/resources/sites/BUSINESS/content/live/TECHNICAL_SOLUTION/77000/TECH77928/en_US/readme_en_338556.html#Whats_New_in_Backup_Exec_12.5
refer the following for version 12.5http://www.symantec.com/business/support/resources/sites/BUSINESS/content/live/TECHNICAL_SOLUTION/63000/TECH63281/en_US/readme_en_308509.html
for 12.0 and 12.5 refer http://eval.symantec.com/mktginfo/enterprise/other_resources/b-bews12.5_upgrade_matrix_081408.pdf
edit @@@the last document referred is probably the best one I could fine to compare the differences.its just that it does not include 2010