I thought VI had replays for campaign battles?

Regardless, if CA wants to foster a healthy multiplayer environment, having a good system for replays is imperative (coming after a good battle engine, mind). Having that means having an active community surrounding the multiplayer mode, able to exist outside the clans as well.

I'd say if they want a greater income this would be the way to go -- instead of selling themselves out to the masses, a great MP mode that allows for easier access through a larger community centered on replays and the discussion surrounding them, and not just clans and their competitions, would attract more buyers. Worked for WarCraft III.