Daring Fireball says this of apps that don’t validate App Store receipts and thus can be ‘bootlegged’

Apple should test for this in the review process, and reject paid apps that are susceptible to this simple technique.

Why? If a developer wants his or her app to be easily run on multiple machines, why shouldn’t they be allowed to?

It’s not the place of Apple to prevent it. Personally I think kudos to Apple for giving developers this freedom.