Initially, no manufacturers were willing to do this. OLPC began designing and spec'ing the initial machine themselves, then worked with an ODM for manufacture. When countries started showing interest, other manufacturers (like Intel) started jumping in to get market share. Once sales commitments hit million unit counts, many manufacturers (ASUS, ACER, MSI) jumped in, later to be followed by OEMs like Dell and HP.
If OLPC hadn't forced the issue, no one would have cut their manufacturing costs and margins to this level.