No, that saves on switching infrastructure and cabling and much more while investing more in wireless access points.

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HERC2 has no effect on eye color, but it contains an unexpressed segment of DNA that is needed for the switching on of a nearby gene called OCA2, as demonstrated by newly published work by Robert-Jan Palstra and others at Erasmus University in the Netherlands.

WSJ: Matt Ridley on Human Culture's Effect on Genes | Mind & Matter

There is no automatic switching, Apple just assumes you'll leave 3G on, and that the iPhone has the juice to support that usage.

ENGADGET: iPhone 3G hands-on Hands-on

No company will be able to justify the cost of switching to the Mac OS on the strength of Keynote alone.

FORBES: Magazine Article