I think the expresion [tex] <0|\phi(x)\phi(y)|0> [/tex]
survives [tex] <0|a_p a_q^\dag|0> [/tex] means:
[tex] <0|a_p^\dag a_q^\dag|0> [/tex]=0 and [tex] <0|a_p a_q|0> [/tex]=0;
only [tex] <0|a_p a_q^\dag|0> [/tex] survives, of course p and q are arbitary,
not single p and single q. the final result will be an integral over all possible p or q.
(2) [tex] <0|\phi(x)|[/tex], is just complex conjugate of (2.41).
there is no special physical significance here, the author, I guess, just mentioned NR
case to make the formula be easily understood.