The first is housing and social services. In the US, social services, especially housing vouchers for hard-to-find apartments are only available to single mothers -- a household with an able-bodied male will almost never qualify. The result? Two-parent households are priced out of the market, as demands for the best low-income is driven by single mothers with housing vouchers. (A poor tenant with a voucher is preferable, because the government always pays the rent.) So we incentivize single-parent households, which are more likely to remain in poverty.
The second is the nature low-wage employment. We expect wage-earners to pay for alot of stuff that is really expensive for a low-wage person to afford. That $20 week health insurance premium with $20 co-pay is expensive when you make $30k/year -- and the coverage usually sucks. In the US, low-wage workers tend to get minimal vacation time as well, so you're basically one illness away from being indigent.
Costs for events that tend to happen are out of hand. My wife found a cache of old bills and vouchers in her office. One was a reimbursement for worker who fell into a hole and broke his arm in 1950, resulting in an overnight hospital stay. The bill? $25. ($135 in 2010 money) In 2011, you'd be hard-pressed to find a motel for that price, and an ER visit for a broken arm would easily cost $10,000.