Do you plan on having a house? If so, will you buy insurance for it? Does having insurance mean that you are counting on having it burn down?
Look at it this way: if the marriage doesn't work out, then he was right to do it. If the marriage lasts until retirement, you have a better retirement than you thought you would.
In real life, the husband would eventually liquidate the nest egg.
A prenup or postnup is insurance - both partners are aware of it and have consented to its terms. Keeping a secret bank account is just being dishonest. I would not look kindly on my husband's actions if he suddenly announced after 20 or 30 years of marriage that he'd been keeping a nest egg from me "just in case."
I have bank accounts that only I have access to, and so does my fiance. We each know about the other's individual accounts. It's his money, and heaven forbid we ever dissolved our marriage, he can keep what is his. Joint assets would be split 50/50, as is fair.
Then again, divorce is not an option for us except in the case of abuse or infidelity. Simply feeling "dissatisfied" or "unfulfilled" is not good enough to dissolve a lifetime committment and a family.
We discussed a prenup, but neither of us has signficiant assets to protect. We're young and fairly poor. ;-)