An interesting note is that small business couples, where the man runs the trade-end of things (physician, skilled trades, etc.), and the woman runs the "managerial"-end (billing, paperwork, etc.) seem to be the most stable of couples.
In matters of money, there are less secrets/unexpected swings; and you both have to be invested in the success of the business, ergo one's livelihood and goal-achievement-vehicle (e.g. for vacations, new cars and appliances, better house, etc.).
Plus, if you cannot tolerate one another and cannot work well together, then you'll know soon enough that perhaps the two of you are not compatible in a partnership (and really, that's all a marriage is if you work for a living -- a partnership to help you both reach your goals).
An added bonus, is that it breads closeness, rather than only seeing your significant other for a few hours every night/morning, and the weekends.
Massive financial/power imbalance? Very. Are both people getting what they want from the arrangement? I would imagine so. The ones that weren't have left/had everything crash and burn, or are on their way.