That's an interesting question. Here is how I see it.
1.e4 : Starts up a more tactical game. Generally speaking, King's pawn games are more aggressive.
1.d4 : Queen's pawn games generally begin calmer than King's pawn games. The tactics don't kick in as quickly and therefore it has been labeled a positional game.
I view a positional game as one where long term strategies are more important than tactical considerations. You can get into such a game no matter how you open but some openings are more prone to evolve into positional middlegames. Maybe someone else can help define this better, I just thought I'd give it a go. 😉
Thanks for that...it does clarify things for me. The idea of long term strategic considerations being more important appeals to me, which might explain why i like to open 1d4. In fact, i always do now. this has the added advantage that i don't need to know king pawn openings as white. Also, it cuts out all the ruy lopez/ giucopiano games which i was getting quite bored with.