I have remarked the same remark, while comparing the specs and the prices of Rugged mobiles used for surveying, this mobiles need to be very advanced in computing level.
this need has brought me the idea, why not use an Galaxy SII or any hi end phone, make it rugged with some accessories, develop a very powerful app, for GPS it could be connected through Bluetooth. these devices containing Dual core or Quad core device could be very efficient at a lot of field operations in no time and at the field. this solutions could be cheaper than those medieval rugged mobiles.