Hi my name is Daniel. Im new to the forum site. I happened to run across your post and thought I'd throw a few words your way.
Apple has done such an amazing job at creating products that "just work" together and work easily. People love integration, especially in the USA, because we always seem to be going, going, going. When you can use iCloud to automatically sync your calendars, notes, contacts, etc..from your iphone to your computer or tablet, it makes life so much easier. As a mac user, I can guarantee you that you definitely get what you pay for with Apple. From Quality to support, the experience is terrific. Am I biased? Well probably, but you have to know this. I was a PC user my whole life up until last year when I purchased my first macbook pro. Let's just say this...I should have made the switch years ago. If you're debating on purchasing a macbook pro, iPad, ipod, or iPhone, don't wait any longer. You will absolutely love Apple products!
However, I will say this...PC's have their place. If you're a gamer, stick with PC. If you're a business owner you could go either way, although the market is dominated with PC's. But, if you're an artist of some type or your hobbies have to do with something of the sort (i.e. music, photography, videography) a macbook pro or mac pro would suit you much better!!
So, to answer your question. Macs are so popular because of their design, their integration with iPhones, their build quality, etc...