I think the way Gadgeteer is set up is to enable easy & quick result for everyone - if you can plug a power cord in a wall socket, you can also connect a sensor/actor to your Gadgeteer board. The rest is software
For me, this type of hardware is just another way to do the things I wanna do; I've now succesfully used a FEZ Panda to do stuff an Arduino can do just as well - it's a matter of picking the right hardware for what you're trying to accomplish. A new platform like this enriches my toolbox and I'm sure it enables me to do things I can't do on Arduino.
Currently I'm trying to get an Arduino 320x240 TFT LCD shield working on top of the FEZ Panda II, but I don't think that the Panda will beat the Arduino (in terms of performance; I've just started with this so concluding may be a bit premature).