The OP assumptions were overly optimistic because it ignored the potential of the money invested, did not account for return of principle and assumed the contract had the same value at the end as at the beginning. He also compared DVC to itself which is a contracted view. I'd say if it makes sense to do that for a few points, it makes sense for more but it really doesn't. If you use better assumptions but the same principles, you'll stretch it out to 12-14 years for most situations, longer for some. It depends in part on what you compared to within DVC and you should look at both the points for a given option AND the cash option for a given situation.
On a more general note, I don't think most people who post these issues really want a full picture. I think most have about made up their mind and are looking for confirmation. Generally they've ignored risk, made assumptions that may be somewhat reasonable but are the most optimistic scenario possible or close to it.