Certified by whom? Is is certified by the manufacturer that it will run Ubuntu 14.04 LTS, or is it certified by Canonical that Ubuntu 14.04 LTS will run on it?
Canonical under Dell name. Even so, I have yet to see the laptop that won't work under Ubunti & derivatives, except for the MacbookPro that required a small tweak in the form of a tiny install from an official repository. You will also see that the Cleco machines only have a few Canonical (Dell) certified ones but that most of their machines have not been tested. As for myself, it does not really matter as, unlike eight years ago, everything just works on Linux. This is true enough to serve as a generalisation. I did experience a Mac wireless adapter that needed a fix in Linux Mint, the adapter is a Broadcomm product. Broadcomm sometimes need tweaking, also in Windows.
The inmortant thing is that hardware drivers for the bulk of peripherals and components come written into the kernel, meaning these devices need no installation of drivers. There will always be an exception, more so with old hardware of a decade ago or so. Even my 9-year old Acer laptop has an ancient AMD Radeon that still is supported by Linux Mint 17.1, the very latest release.
On both Mac and Windows, my own personal experience is that peripherals will work on Linux (Debian/Ubuntu family) but then not on these two major OS's. I even had to go buy new devices to please 64-BIT Windows and Mac just failed to accept each and every USB HSDPA dongle that I had. All these worked fine on Linux.
Mac had compliancy issues with its own OEM branded products! My Macbook pro just as my iPhone 5 both rejected the original cables and chargers they were shipped with, over and above the third party devices. Mac updates also stopped wireless networking on my iPhone. Mac hardware is top quality and its super smooth software is marred only by Apple staffers who roll out broken updates. Otherwise, a most pleasant product to be working with.
Also printers: ask the techie at my local Incredible the many comebacks they had on HP peripherals that had inadequate drivers for 64-BIT Windows 8, same as I had seen on 64-BIT Windows 7.
I think that more than three decades on the field had taught me something. I hardly ever deal with opinion but rather stick to facts, especially when repeated personal experiebce can confirm. It is ludicrous to even think that Mac is 100% hardware compliant. Even their own dealers are, to this day, reluctant to recommend scanners, printers, MFD's, etc.