I just wished that the designer hadn't put that block of pins on the Uno off grid by .05"... That makes home cloning hard. Maybe that's the reason...Massimo is afraid of "Cottage Competition"..
Sorry for the soliloquy about "Home Made"..
It wasn't a conscious design choice, but rather a error made on rush of ordering of the first batch of PCBs of the original arduino board. Once released and 3rd party shield developers began to ship they didn't feel it would be right to 'correct' the non-standard spacing and make all older shields incompatible.
Lefty