And if you can't get access to social services in Beijing, are you really a beijinger? Where do these kids go to school, take the gaokao, have a higher chance to get into PKU or qinghua? You aren't a full beijinger without hukou. That we can get hukou for a few of our college new hires every year is a big recruiting advantage for my company.
True. Actually there's been ongoing discusses on this issue, about education of children of migrant workers in China.
You cannot purchase a house, send your kids to school, or access many social services without a Beijing hukou(something like resident identification).
Big tech companies like Microsoft and Sina becomes more competitive on recruiting, because they have been given some hukou credits by the government, so if you get into these companies, you can get a hukou when it's your turn in the long-long queue.
And local Beijingers do not welcome those migrants. They even think it's unfair to let the kids of those to receive education in Beijing, not to mention the college entrance test(aka GaoKao).