Jay Honeck wrote:
"If Microsoft built the X-Box the way Garmin built the 496, they'd
have sold about five of them..."

But they have very few engineering requirements in common:

One has to run on batteries as long as possible (i.e. low power draw),
include radio receivers, be as small as reasonably possible, and must come
with its own display.

The other can draw as much power as it needs, has no physical size
constraints on human interfaces, and requires an external display that must
be supplied by the user.

The closest comparable consumer products with equivalent engineering
requirements that comes to my mind is the just-released iPhone and
notebook/tablet computers.