I found this page on hardware enablement. My understanding is that new hardware isn’t supported with old kernels, which older LTS releases are stuck with. So Ubuntu solves this problem by backporting newer drivers to the older kernel release.
That’s quite an interesting way of making money. I guess if Dell wanted the newer drivers, they could just install a newer version of Ubuntu. But since they wanted more stability, they preferred that Canonical backport the fixes to an LTS release.