We don’t sell the 1.7.x version directly, instead we make available EE 1.7.x for those who want to stick with EE 1.x for one reason or another. Often times it may be because they want to use third party addons that aren’t available for EE2.x yet.
As time goes by, we won’t offer or support that older version. That hasn’t happened yet, but it will eventually.
When you purchase EE 2.x, you receive a single license number. Not two different ones, just the single number that will work for either 2.x or 1.x.
EXPRESSIONENGINE INSTALLATIONS
ExpressionEngine Installations: All ExpressionEngine license purchases allow a single “live” installation in a production environment and ancillary “development use only” installations as needed for that support the live installation (such as development and a staging servers). Additional installations require additional license purchases. If you have specific installation needs not covered by this license, please contact us (http://expressionengine.com/support).
If you are going to be reselling licenses, you’re better off with EE2.x as eventually there will be no official support for the 1.x branch.
As far as selling 1.x licenses go, I’ll mention it to Leslie Comacho this morning when he comes online.