"Unsurprising perhaps is the dominance of Linux in this space"
Actually, while not massively surprising, I do find this interesting (and yes, a little surprising).
I have been writing embedded software now for about of 20 years. While there is no doubt that Linux is starting to make inroads, it is only relatively recently, and there is an awful lot of embedded stuff out there running on other (usually much smaller) OS's. You seem to only mention the "larger" OS's (like Linux, Vx Works, OS9 etc), presumably leaving the small embedded OS's like Nucleus, pSOS, and the zillions of in-house kernels to the "others" section. I would expect the use of these OS's to dwarf the use of Linux in the embedded world. I would certainly not consider Linux "de facto" in the embedded environment.
In a true embedded environment, you usually do not need or want the sophistication of something like Linux - it is a large and complex system, which you can usually do without. The other biggie that you seem to be forgetting is that Linux is NOT a real time OS. UNIX (and I include BSD and Linux in this) has never been real time and is very unlikely ever to be. Yes, I know there are "real time" versions of Linux, but these are still often not "real time" enough.
Basically, you seem to be looking at the embedded world as if it was just and extension of your quad-core Xeon desktop PC, and this, is simply not accurate. This is (almost) the case with devices like the latest mobile phones or pocket computers with their MBytes of storage and processors faster than your desktop was 5 years ago, but devices like these are not really "embedded" any more - they are just "normal" computers running (almost) desktop applications. They're just smaller, that's all. It is precisely this muddled definition that allows "Windows CE" to be included in your survey at all - nobody in their right mind would use Windows 'anything' in a true embedded device - it is a non-starter (it's size and complexity alone would preclude it, never mind it's shockingly bad reliability record and the fact that it is basically rubbish).
I have used Linux in embedded environments in the past, am doing so now, and will no-doubt continue to do so. But the systems involved require the sophistication that Linux provides (usually boiling down to its networking support), and, of course, it's cheap! I'm not knocking it at all, but I do think it is a mistake to think that Linux is taking over the embedded world. It may be in some areas, but for each that it is, there are a million others that it isn't.