p.s. BTW, there's a book, I can't remember its name, but it describes how WinCE got started, and explains how it developed. It started from a clean sheet, using the Win32 API, but none of the code at all. It was originally quick, light-weight, clean and elegant. The designers deliberately wrote only the necessary stuff for an embedded OS to work, and kept it modular; by writing from scratch they intended to learn from the mistakes of Windows but keep the best of the ideas.
Only when people persistently asked for new bits of the Win API to be put in did they did so, however, as time went on, the demands to keep bolting new bits in took off and it grew fat and bloated.
In theory, as I understand it, if you're a device developer, you can still build a minimal WinCE system which is sleek and quick, but in practise every device you can buy has to contain the full system build to be labelled Windows Mobile and is thus slow and bloated.