Apple probably doesn't think that you will pirate it but I think they have made this move simply because they've already made their money off of you. If you own a Mac, you've already paid the Apple Tax. The proceeds from small purchases like this and the Apple Stores go to 'the steves' private jet. It eats alot of gas.
Companies like Adobe and MS are different. Their sole business (with few exceptions) is software. Both companies have sizable, very powerful anti-piracy teams, but why go after individuals. In most cases, these teams go for compliance of big companies where serious infraction occurs. If someone pirates photoshop, 9 times out of 10 they aren't very good at it and don't use it for a living. If that were the case, they would more than likely, when they could, pony up the funds so that they can participate in upgrades, beta tests and customer relations. Most college students probably 0dayed CS4 for bragging rights and probably won't have the time to harness the capability of the entire suite when used in a design house.
Same way with MS, more or less. All OEM boxes come with a copy of Winblows anyway, and of the small number of those who build their own boxen, an even smaller percentage of those will put fourth the time and effort to pirate the goods.
When Apple removes their anti piracy mechanism from Aperture or any other Pro apps, then I will be impressed.