Originally posted by tvochess
This is a plausible explanation. But why is that?
According to BigDogProblem, e4 is more drawish on the GM level because of the Berlin Wall, but that is in the Ruy Lopez only, and I think one of the reasons the Sicilian became popular (which is still an e4 opening).
Someone else mentioned that he/she considers e4 to more difficult to play because of t ...[text shortened]... es.
Bonus question: how to play d4? what should a d4-player aim for in the first 10-15 moves?
I think there's a few of reasons why e4 is more popular than d4 with weaker players. The major one is that GM's are professionals and the rest of us are amateurs and tend to have to specialize to cut down workload. So there tend to be relatively few amateur players who play both 1. e4 and 1. d4.
So the next question is why e4 and not d4? I think you are basically right, I think that by the time someone is going for opening specialization they are generally not pushing their pawns forward the way some complete beginners do. So I suspect that a major one is that the e4 openings tend to allow quicker attacks. It's just easier to understand where to put your pieces. I think that it's just that the d4 openings are technically more difficult. There are traps all over the place and white can't really avoid theory. I think beginners often want to specialize as they improve and e4 is the more likely choice.
Personally I started playing e4 exclusively to force myself to cope with openings tactics in every game, which was the right thing to do then, but in the meantime it's become a bit of a habit. It also meant I only had to cope with one set of defences, I also always found the Nimzo-Indian difficult to deal with. I'm trying to understand 1. c4 at the moment; I've played 1. d4 and although my overall results are about the same for 1. d4 and 1. e4 I found that my results with 1. d4 are worse against better players (>1,800) than my results with 1. e4 - which is weak evidence for my notion that weaker players find 1. d4 games harder.
As far as your bonus question is concerned, it depends, but after 1. d4 and 2. c4 white's got space on the queenside and needs to look to exploit it somehow. A queenside attack may be the way forward, another potential plan is to try to give your opponent an isolated queen pawn and attack it, or try to obtain an IQP and use it as a battering ram. It depends on what black does. It's not that d4 openings are more sophisticated than e4 ones, it's just that it's harder to avoid having to use more indirect approaches than in e4 openings.