MITM the http connection you used to download truecrypt?

I assume MITM your https connection by manipulating CAs.

Or use one of their 0days to breaking into your machine and get your data while it is decrypted in memory or just steal your password.

Do you mean "NSA has stockpiled vulnerabilities they've discovered in Win8 that would enable them to quickly enroll a networked Win8 box into a C&C"? If so: sure, I agree.

Do you mean "NSA has implanted backdoors into Win8 that would enable them to directly enroll a Win8 box into a C&C"? If so: virtually nobody who does professional vulnerability research, myself included, agrees.

The distinction matters here, because if all you're saying is the former thing, that impacts Truecrypt just as much as Bitlocker, because it's equally true of every operating system, including Linux, FreeBSD and OpenBSD.

This seems silly, but Microsoft appears, on the surface, to have purchased Skype with the intention of selling surveillance to the NSA. They immediately replaced the whole network architecture and encryption setup with something that had weaker security and was subject to compromise of Microsoft.

That's the sort of player we're dealing with, and that's why Bitlocker is not just improvably secure, it is best to simply assume that there are deliberate backdoors, whether any particular employee knows of them or not.