Your point relies on a significant number of users caring about such things, but empirically, they just don't. No number of car analogies will make GPL-style software freedom meaningful for the vast majority of people.
Do you remember when Internet Explorer was the only kid on the block, and then Firefox came out and was a breath of fresh air? I know a lot of non-programmers who cared about that, and that's a direct result of the ability for anyone to modify software. Remember that Firefox was based on Netscape, which had previously been knocked out of existence by IE. The difference between Netscape and Firefox was freedom to distribute modifications, and that made a lot of difference to a lot of users.
