The keys are already big enough, so it's not a strict improvement and even if bigger keys are better, why are the up/down ones less important than left/right? If anything I use up/down more, because I use them for both reading and writing, whereas left/right are almost exclusively for writing (would be more so were it not for the lack of consistent PgUp/PgDn shortcuts on OSX: these are sometimes bound to left/right and sometimes to up/down depending on the application).
Having used both types of key arrangement (and others) on various cheapy Windows laptops, I know that for me at least, the inverted-T (without extra keys crammed into the spaces) is absolutely essential to being maximally productive at the text-related tasks I spend 95% my time doing. I can adapt to a 3/4 size keyboard more effectively than I can adapt to a full-size one without the inverted-T.
Could you elaborate on this aside? To me, it looks like a strict improvement on the arrow keys since the up/down keys are identical and the left/right keys have simply been embiggened (stretched upwards). Or do you think the negative space above the left/right keys gave important touch feedback?