IIRC, Windows a) builds a list of files to pre-load from disk based on your usage, and b) doesn't actually fully shut down by default (it goes to hibernate mode: http://blogs.msdn.com/b/olivnie/archive/2012/12/14/windows-8...). I don't know if any Linux distros do either of those by default, but it is certainly possible.

Also, some BIOSes already have a "quick boot" setting which caches some hardware information, particularly about memory. It usually comes with a warning that you need to disable the setting for at least one boot when installing RAM.

The holy grail would be a kernel organized and designed to cache everything to disk related to its own configuration, and only re-execute/rerun the hardware reinitialization code.

Admittedly, Windows' current approach to bootup is very close: it closes all applications then pseudo-hibernates the kernel. Bootup simply reads the hibernated kernel state from disk and reloads userspace.

This is of course besides traditional full ACPI hibernation, which is pretty cool but isn't a perfect art. (I'm typing this on a ThinkPad T23, a fairly old (and thus well-tested) hardware configuration; its hibernation/resume is usually rock-solid, but this morning my WLAN decided to get all stupid with dhcpcd, and USB decided that while it could see my external HDD, there wasn't a disk inside it. From-scratch boot is still the only way to get a reasonably predictable system state.)

In the embedded hardware environment if something has changed and if this change is out of specs, then what you say can be adopted.