Early this month Facebook and Twitter ended several weeks of discussions, in which Facebook was offering to acquire Twitter for $500 million of its stock, reports Kara Swisher on AllThingsD.com. Part of the rub was price. But, perhaps more important, “was a feeling among Twitter investors and execs that the start-up should still take a shot at building its revenues — there are none right now — as well as it had done at building its growth,” Swisher writes.