The Vytec manual that I have was printed 5/2002, and the computer itself appears, from the serial number, to be one that was manufacturered within the last 3 months or thereabouts.
It has the unit selection option.
My Vyper was bought in July. It too has the unit switching option. Its serial number is significantly lower; I don't know when it was made. It may have been on the shelf for a bit.
The deletion of this option may be an attempt by Suunto to stanch the flow of units from the EU into the United States and protect even further their price fixing here, since in the EU this kind of price fixing is flatly illegal and the law is actually enforced over there.
If so that sucks.
Upon more review, however, I suspect its a model differentiation feature. The online versions of the COBRA and VYTEC manual both still show the option.
Perhaps this one of those "features" to get you to move to the Vytec, kinda like the RGBM50/100 switch?
(BTW, you can change the sample time on the Vytec from the computer - you don' t need the interface. Yet another difference.)