Ubuntu's avowed mission is to bring Linux to the Masses. For the masses, a computer still "looks" like Windows. Ubuntu being a Funded initiative unlike Arch(my choice), Gentoo, Crunchbang et all needs to fund the development of typography on Linux.
Yes, its possible to download msttcorefonts (with some creativity you could also get the Consolas set of fonts) and get Cleartype or Os X type smoothing - but as long as its not the default , i am afraid there is no pushing Linux onto the masses.