I really liked Twitter prior to 2010 when it got too popular/noisy. (That was partly my own fault for following too many people.) But to your point, I think that another reason the G+ Twitter comparison came up initially was because FB didn't have the "subscribe" function it now has. Essentially, circling someone on G+ allows you to subscribe to their public posts, like FB also now allows you to do. You don't get to see their limited posts unless they circle you back. Unlike twitter, circling someone also allows you to share with them (via the "incoming" feed), if you so choose.