They design it like this so that those less comfortable with tech are not intimidated by it (which is ultimately where the big money market is right now).

I had to give my mum literally zero instruction in how to use iCal on her iPad,she uses outlook at work and still forgets how to do somethings. When I showed her iCal in lion she said "it looks just like my iPad one - I'll be fine".

When showing the older generation round Apple stuff I find there is a strong correlation between how "life like" the app looks and how easy they find it to get up and running.