The formal federal poverty level is $22K for a four person family. If you earn that amount or less then the federal government will "officially" count you as poor and there are certain federal or state programs for which you are eligible.
Of course it's a sliding scale and the family of four that earns $30K may not
officially be poor according to the federal gov't but they will still barely be making ends meet and so will have partial or total eligibility for certain programs.
As you state there are plenty of people that earn less than $88K and who are not poor. This is why $88K is 400% of poverty level and is where the Senate/House bills would phase out assistance. It's how they got the cost numbers for the bill to work.
However I would venture to guess that a family of four that brought in $88K (whether it be two people earning $44K or one person making the $88K and the other staying home) would not have the funds to make a required and unsubsidized purchase of health insurance at $15K/year. The number of people that fall into this category may be small -most folks are employed and get insurance through their employer- but it would be a hardship.
The other thing is that the buying power of $88K in 2010 is not the same as the buying power of $88K in 2000 and so on backwards. 10 years ago I thought that if I could just make $X/amount I'd be on easy street. Well I make that now and on easy street I'm not...