I'm not convinced it's that big a deal, although if they can sell it for £5K then good luck to them!
I build little embedded(ish) systems myself - AMD Geode boxards (ALIX) and my custom compiled kernel boots in 1.08 seconds (according to kernel output) If I didn't compile in networking and USB, I'm sure it would be under a second.
The biggest time is the boards BIOS (5 seconds), then loading the image off flash then the kernel uncompressed and boots - 1.08 seconds.
If I had more access to the board and had 4MB of flash ram as part of the memory map, then I could eliminate the long BIOS + Load times and jump into kernel on cycle 0. That's where the trick is, I guess - a fast load of the kernel into RAM, or keep it in FLASH that's part of the memory map.
After the kernel is loaded it's just userspace - I run a cut-down system, but it still takes another 15-20 seconds or so to get time, dns, networking, apache, etc. going. You're probably not doing that with an in-car device or a camera, etc.
So it's not really hard to make a kernel boot fast and possibly even launch one application - the big savings are going to be on the hardware when you can eliminate BIOS and load times, and the amount of userland you then have to load - which is the real difference between "embedded" and general purpose (e.g. desktop)