Another vote for the broadest view possible - consider all accounts for both partners. There may be lower fees for the same class of funds in one of those accounts. Perhaps one works for a large employer that has qualified for lower institutional fees and the other doesn't so would have much higher fees for the same exact fund or category.
This has always bothered me about some online 'retirement' calculators because it's only about that one account and one half of the couple's assets. You know, with many people changing jobs so often - most people do not have all of their retirement savings with their current employer. I believe Fidelity, for example, now lets you add additional accounts so that you can look at all of them at the same time. Of course, like mentioned above, tools like SigFig and Personal Capital also let you add multiple accounts for both spouses (or partners) as well so you can see what your overall investment portfolio really looks like. We like this!
Still, I think Mr.Need2Save and I still have small differences in what we mix we are comfortable with and that comes out in what each of us owns within those accounts. It's a good conversation starter.