but since the Surface Pro is really underpowered for a general purpose dev machine, it's kind of pointless. basically paying lots of money for a machine that's optimised for low power, low weight and ultra-portable, and then asking it to do CPU intensive things whilst plugged into a docking station, which seems a bit like a waste,
It has an i5 (IvyBridge) and 4GB RAM. Why wouldn't it perform well for general development? Unless building a game engine is part of your definition of "general"...
But, your main point stands...if all you're going to do with Surface Pro is sit down at a desk to code all day, you'd might as well get a PC which would be cheaper and much more powerful.
Though, I'm the type of person who'd want to move around and hit the coffee shops to work on stuff. For this type of scenario, a Surface Pro would be just fine (though, an Ultrabook would work as well).