Article claims the reason is so that the videos will play on iPhone. If Apple considers people who already own an iPhone most likely to view the page and buy the newer one, it makes sense that they'd go through a lot of work to show them animations they couldn't through the video tag.
Preventing download and viewing doesn't seem very important to me. Anyone could just use one of many screen recording apps to get good enough copies anyway if they wanted them for some reason, and who cares if they do have them.
