As far as I'm concerned, the bursts detail themselves enough for satisfaction (as all directions includes up and down).
As for blasts, you could apply the same reasoning thus, so a blast 3 is a 3x3x3 cube. However, this means you have to apply this to creature size (so large creatures are 2x2x2), and it enables a PC to use a blast effect from the upper square over some friends against a Large or larger foe. You may want to house rule that a cubic blast has to include any square adjacent to a PC on x or y axis, not just any adjacent square.
It's a fixable problem, but definitely a major oversight on the part of WotC. It doesn't do much to improve the edition's growing infamy.