Why do websites in the US ask for a promise that you won’t export the computer outside the US? Better put: why does the law require them to ask this?
It’s not the hardware, but the software preinstalled. Modern browsers contain strong encryption for secure transaction. Strong crypto cannot legally be exported to some countries from the US.
Sample export notice for those wishing to use Netscape:
Licensee agrees to comply with all export laws and restrictions and regulations of the United States or foreign agencies or authorities, and not to export or re-export the Product or any direct product thereof in violation of any such restrictions, laws or regulations, or without all necessary approvals. As applicable, each party shall obtain and bear all expenses relating to any necessary licenses and/or exemptions with respect to its own export of the Product from the U.S. Neither the Product nor the underlying information or technology may be downloaded or otherwise exported or re-exported (i) into Cuba, Iran, Iraq, Libya, North Korea, Sudan, Syria, Serbia, the Taliban-controlled areas of Afghanistan or any other country subject to U.S. trade sanctions covering the Product, to individuals or entities controlled by such countries, or to nationals or residents of such countries other than nationals who are lawfully admitted permanent residents of countries not subject to such sanctions; or (ii) to anyone on the U.S. Treasury Department’s list of Specially Designated Nationals and Blocked Persons, the U.S. Commerce Department’s Denied Persons List, or the U.S. Commerce Department’s Entity List. By downloading or using the Product, Licensee agrees to the foregoing and represents and warrants that it complies with these conditions.
Source: http://wp.netscape.com/download/client_netscape6.html