On the first point, this is the behavior (and naming) in ST and Ace (though it's slightly different in Ace: it always uses the anchor position regardless of whether you're adding up or down, whereas ST uses the beginning of the selection when adding up and the end of the selection when adding down). 

The standard use case seems to be when you quickly want to create a vertical set of cursors without having to use the mouse. I could imagine that we change the behavior when you have a range on a single line to add a corresponding range on the next line, but by default I thought it was best to match the ST behavior since I'm not familiar enough with people's multiselect workflows to know what behaviors they depend on.

The behavior in the second case also matches ST, but I think it seems less weird there because Sublime always shows a cursor on the anchor side of range selections, so you can actually see a cursor at the beginning of the next line. It definitely feels weirder in Brackets.