[Rant] diff between dch3416 and dch 6416

I have a dch 6416 that I'm, renting from metrocast, I'd like to buy my own, and have seen a couple of dch3416's on ebay but need to know what the difference is?? I've read that the 3416 only has a digital tuner. Since all signals are supposed to be digital now, what's the diff??, I get digital cable from my company so shouldn't that be enough?? Regards, Rich