I saw a tweet about this and the answers back were wrong, so here’s the correct answer, as I understand it, both from having worked in stores and now, seeing the process from this end.
1 - Retailers take Monday to recover from the weekend: clean up the shelves, and most important, reorder the hot sellers and sold out items in time for the end of the week and coming weekend. This is also the day that store managers are deep into running critical and essential sales reports.
2 – Tuesday is a relatively slower sales day, so the store staff can focus, especially in the morning, on checking in, stickering, and putting out the hundreds of new releases, whether they be books, cds or dvds. Additionally, the store manager can schedule enough people every Tuesday, knowing this is the industry-standard on-sale date, and also have the staffing for the customers later in the day who want the latest release(s).
3- Tuesday on sale has the added benefit – vs. Wed. or Thursday – of having the maximum time for new items to be on sale, so that the first week’s sales are substantial, which the retailers and publishers and movie record companies want.
4 – So why not Monday, besides reason # 1? In order for the items to be ready Tuesday AM, they are usually delivered Monday, but held in back and not put out. If Monday was the on-sale date, items would have to be delivered the Friday before, and then the temptation to put out the much-anticipated items would just be too great, resulting in chaos and a lower # sold in, technically, the first week.
5 – And yes, a few huge releases do have a Monday release, due to expected weekend media, like 60 Minutes or a Friday magazine cover store. Those boxes are stickered with glowing neon stickers and retailers know they will lose the next big release if they break street date that weekend.