It defintely does deltas but see SebastianZ's explanation
https://www-secure.symantec.com/connect/forums/liveupdate-administrator-and-delta-updates#comment-8487571
https://www-secure.symantec.com/connect/forums/lua-and-deltaupdates#comment-8358581
Also see Mick2009s article:
https://www-secure.symantec.com/connect/articles/how-big-are-current-symantec-endpoint-protection-definitions