If you compare the relative complexity of games made now to games made then you might see a slightly different story. Creating a modern game is a ludicrously expensive endeavour that can take years and dozens of people, whereas in the olden days three people in their bedrooms coding in their spare time for a few months could crank out a classic. Now, if your expenditures are very small, you're willing to take risks and try and do something innovative, because even if you fail, it will not affect you badly. However, if you're spending huge sums of money on a game, you need it to be fucking bought. The majority of gamers today are scared away by things with a whiff of complexity, because they've grown up on consoles.
Although in the complicated turn-based strategy department apparently Sword of the Stars is pretty good.