Vs. 1.e4

No. What you mean is that you can play moves like 1...d6, 2...Nf6, 3...g6 and 4...Bg7 against much of anything. That's not necessarily a Pirc though.
Especially when White's c pawn isn't blocked by a knight on c3 (say, after White's 1.d4 and 2.c4) then play is completely different because suddenly White has a strong plan on the queenside and it makes sense for him to close the position.

No. What you mean is that you can play moves like 1...d6, 2...Nf6, 3...g6 and 4...Bg7 against much of anything. That's not necessarily a Pirc though.
Especially when White's c pawn isn't blocked by a knight on c3 (say, after White's 1.d4 and 2.c4) then play is completely different because suddenly White has a strong plan on the queenside and it makes sense for him to close the position (it has downsides for White as well).
Yes, Zirtoc is right. There are certain lines in the Pirc where black plays c5 and gets a Dragon like position.