Re: Spartan won't support ActiveX controls or Browser Helper Objects
"You could remove IE as far back as Windows 7, but certain parts of it shares code with the OS."
Afraid not. You could "Turn Off" Internet Explorer in Windows 7, but it was still staged into Windows Side-by-Side (WinSxS) component store, ready to be re-deployed. That's part of why Windows 7's footprint is 16GB - the Windows component store.
Furthermore, the code that it shares with the OS itself is fairly minimal if reports are to be believed these days post-IE6. Its rendering engine (MSHTML.dll) is left because there are so many applications that expect it these days. It's pretty much impossible to remove IE entirely without breaking a ton of non-default applications but not necessarily Windows itself. That said, I've never looked at the source code and can't verify if any separation has actually occurred.