You can play without the keyboard but there are hotkeys, they are remappable and by default they use spatial mnemonics instead of letter mnemonics.

Even though we intended for keyboard support, its a good design philosophy to design it for a mouse because it helps keeps things organized, symmetric, transparent and accessible. The number of options on the keyboard can make it very easy to lose control over each of these categories and you are more likely to end up with a sloppy mess that confuses, frustrates and annoys people. Only the hardcore players will stick with it.

Psychology studies on spatial mnemonics seem to give better results, and I know personally it works better for me. The idea is that you can see on the screen where the button to attack is (say 1,2 in the action grid) and that would correspond to the same grid position on your keyboard (or A in this case). We've organized it primarily for the wasdf left hand position that most people who play first-person shooters are now very used to and it provides a fair bit of flexability and accessability (which is probably why fps games use it in the first place).

Sins GUI   Keyboard
12345  ->  qwert
12345  ->  asdfg
12345  ->  zxcvb

The other idea is that buttons that do the same or similiar actions will appear in the same position across multiple units and across races.  The button to build the basic scout unit for example will always appear in the same location even if the unit building it is different and the unit being built is different.