Why? for $900, it seems to offer more than a baseline MBAir (better processor, screen). But with some added touch, especially the pen input (something I'm curio

Why? for $900, it seems to offer more than a baseline MBAir (better processor, screen). But with some added touch, especially the pen input (something I'm curious to how well it works) in a tight tablet form factor. I'm curious as to whether I'd be able to plug this into my large external monitor and do my day job with it.