It's true that vitamin C helps absorption, but you still get way less than from red meat. Humans have a haemo-transporter to get the iron into our blood - but it only works on iron in the form that it's in red meat (and breastmilk!). Spinach (and eggs are the same!) is an interesting one too, as while it is is high in iron, it also contains a substance that reduces iron absoprtion.