The canonical <CR><LF> in rfc2015

[Hiroyuki.Yamada@xxxxxxxxxxxxx (Hiroyuki Yamada)]

I have a question about PGP signed data in section 5-(1)(2)(3)
of rfc2015. It requires <CR><LF> for end of each lines instead
of <NL>.  

Could anybody have any reason for it ?

Thank you,
hiro