since the xbox, and passing trhu the app store (e.g. FTL is 9.99 drm free for 3 platforms, vs appstore 9.99 for a single device). everyone with half a brain knows buying online is never the best option. xbox FPS games are around $20 on target and the like. buying on the live network it is $59.99.
I would say the 90 days is the "evil" option, because it makes the others seem like a bargain.
There's a lot of psychological in in sales because it's almost impossible to "value" something. All you can do is to compare it to market prices.
I especially like the "and get something extra for FREE" trick. :P