Trouble is, it's not "just" DI.
It's Dark Intent, Curse Of Elements and Demonic Pact (10%SP)[yeah i assume 90% of the locks are Demo nowadays, my guildmate is so...:P].
Sometimes i miss both lock and mage in raid, with no shammies healing either. It's way more then just 2.5k...WAY MORE.
Btw, as Zuiza said, it's just for vanity...but i'm pretty in love with BIG recount parses so i'm quite sad raid setups are so screwed in 10m enviroments. Really looking forward for 15m, and i do hope i'll see that in 4.3 (very much unlikely but dreams and hopes are free).