I am now calling the Apple to find out.
The salesperson I talked to could not provide me an answer (He had not encountered such a situation). When I was transferred to an expert, the telephone line was interrupted.
I guess that it all depends on if the buyer is able to download Lion for free from the App Store after buying a Mac. If the buyer can download Lion from the App Store for free, then he/she can then download Lion and make an Installation DVD or an Installation USB stick per instruction given on the FrontPage of macrumors. And then he/she can install Lion on all his/her Macs using the Installation DVD or USB stick.
I talked to a gentleman from the tech support and was told that there will be a Lion USB stick coming with a new Mac Mini (for example). But this USB stick can not be used on other Macs. However, I doubt it. If this USB stick can be used on other Macs, we can then use it to install Lion on all other owned Macs. If not, we have to purchase Lion from the App store.
Any other way out?