...Sins Of A Solar Empire sold very well and famously has no copy protection at all.
This isn't the case - Stardock do implement DRM (online activation) in their games (and Sins
does require activation) but it is added via patches (see
this thread for related discussion on Sins). Now whether you consider this "customer-centric" (Joe User can choose to stick with the initial buggy version without DRM) or "bait and switch" (allowing Stardock to enjoy "DRM-free" publicity while slipping it in later) is a matter of personal opinion. I however boycott Stardock zealously having been "bitten" with GalCiv2 (and since I was a former Object Desktop consumer, I can comfortably say that they have lost $100+ of business as a result).
Any arguments about "DRM reducing piracy" need to consider how easy the checks are to circumvent - online activation is not intrinsically any harder to disable than a media check so online DRM will be a negative factor if costs (increased support, reduced sales due to consumer protest, third party fees) aren't covered by increased profits.
However one key issue affecting profits isn't piracy - it's the savage discounting at retail many games receive after just one or two months (in the case of Iron Lore's TitanQuest, I purchased the Deluxe Version for just £7/US$11 7 months after release). Given that many games require one (and sometimes two or more) patches to fix problems, this provides a double incentive for purchasers to hold off for a couple of months.
In fact, dealing with piracy is very simple. Release a crummy game, and few will bother to copy it. It is increased sales that developers should be aiming for, and treating paying customers with respect and doing everything feasible to make their gaming experience a pleasant, care-free one is the way forward - not making them jump through hoops, adding software/hardware incompatibilities (*cough*
SecuROM *cough*) or limiting the lifespan of their purchase.