GPLv2 just requires the sharing of source code for a given binary. GPLv3 takes it a lot farther and requires that a mechanism also be provided to use derivative works. So if a car manufacturer uses GPLv3 code, they not only have to distribute the source code (which may or not be an issue), they also have to allow people to flash their own code onto the car's embedded computers.
This problem stemmed from TiVo, they used GPL code on their set-tops but signed their binaries. People could make derivative works, but couldn't use them.
In the embedded space, you can imagine that GPLv3 is very much hated. It's a big reason why a lot of projects haven't switched to v3.