Well I have used a 338 on deer before, and I would have to say,,,"why not"
My first rifle was a 30-06 and likely would have served me well for everything I was intending to hunt. But a dozen or so rifles later, I still haven't fulfilled my whims. Alot of this is "just because factor".
I personally prefer .25 cal. and over for deer, but I don't question the next guy's desires, whom uses a .243/6mm cal.
Again, I think the 338Win Mag is a splended round, is it needed for deer, hell no!, is it wrong to use on deer, hell no!, would I shoot another deer with, hell yes!,,,,why not?