Obviously, in case of full disk encryption, the bootloader needs to be able to do decryption. If not, the disk would be unbootable.
Sure, the text now trivially identifies the disk as 'truecrypt', but even without that text in, it would not be hard to detect a specific bootloader with signatures...
If one wants deniable encryption you need to use something else than full disk encryption, such as steganography or hidden volumes.
