You can say that the Star Wars titles just fell into marvels lap but it really does not change they have done a great job with them. Quality aside there is no denying the Marvel titles inn general is placing better in the charts then Dark Horse ever did. Thats just a fact. I never read Dark empire but I will take the recent Darth Vader series over most of what I have read from Dark Horse. Dark Horse did some good stuff but there are also plenty of bad older stories that have such bad art I know I am never going to be rereading those.
I see no particular reason why Marvel would drive Star Wars into the ground before DC reaches a point where Batman will stop being AS big a seller right now. I think its unlikely that readers will continue to buy this many Batman books and one shots.
I also see no real reason why that argument should count just because DC created Batman 75 years ago. Its not like those creators are still around either.
Besides if Marvel were not dedicating resources like writers and artists to make these book as succesfull as they have been then that is work that would have been used on other titles.