I don't think it's the build vs. buy trade-off, I think it is more a question of efficient platforms for vendor collaboration resulting in the emergence of voluntary standards that create efficient and open markets kind of problem. Ruby has a DIY ethic which is respectable, but there's little infrastructure to support market-wide discussions throughout the ecosystem.

Really, if you want to make analogies. Rails is essential loose federation covered under Articles of Confederation while Java is to be appreciated as a strong Federal system that allows for states to innovate.