In fact, I understand why it does this. If you don’t have a mouse (ok, uncommon, but still), you need a way to perform the same actions with the keyboard as with the mouse.
X allows to simulate the mouse pointer (with the numerical keyboard) so it’s a different approach.
If you want to cherry-pick items without using a mouse, it seems it’s not possible with Mac.
If you hold down Ctrl + Shift under windows, and then navigate with the keyboard, it acts like if only Shift was used.
If you hold down Ctrl, up key moves the selection overlay. If you release Ctrl, the selection overlay stays here, you can press space select it.
If you select the x-th file and then navigate to the y-th file with Ctrl down, and then, hold Shift down, it selects all files between x-th and y-th.
There is a difference here with just holding down Shift + navigating, as Shift select all files between the first and the current position.
For example, if you choose to display your icon as a grid, let’s say 6x6 items are displayed, and select the one at pos (3, 2), holding down shift and going to (4, 3), will select (3,2) (4,2) (5,2) (0,3) (1,3) (2,3) (3,3) (4,3).
If you do the same thing with Ctrl down, and use shift for the very last move, the selected items will be (3,2) (4,2) (3,3) (4,3) (that is: all the items overlaping the rectangle made by the 2 selection corners).
It’s hard to explain, but a bit intuitive to use in fact (still, I’m not using this myself, the describtion above comes from my first test after user reported the behaviour he expected).
I admit, this means many states to track if you want to emulate such a thing.