well Marvel's big cross over event has sold a lot more copies then DC cross over event
people on the net are giving there reasons.
Secert Invasion had more multiple covers
Count Down sucked and so everyone is scared to pick up Final Crisis
There is a large anti Morrison fanbase (who are these sick people?)
put looking at the over all sales chart I notice that Marvel in general seems to be more popular then DC. the majority of the top 20 comics are from marvel...actually most of the top 50 books seem to be from marvel.
I think a big factor might actually be that their are more Marvel fans in this current comic book market then DC fans. So with both companies having big cross events at the same time you can expected marvel to have higher sells because marvel in general has more fans.
I think that is the base of the problem (though I would be suprised if some of the things I listed had some effects on sales)