Well it's kinda like the Apple argument...I just think they do it best. Resizing is automatic, licensing of your choosing, visibility options, HTML codes to plop pictures on the web, slideshows, great integration of tools, lots of apps to play, and free editing using Picnik, plus integrated printing. Sets, collections, galleries, tags make it easier to catalog a lot of work. Many others who share the passion contribute and make my experience better as a photographer. A wonderful Explore page to see the daily best work. I pay for premium services and have 18,000 plus photos stored in the cloud. Good thing since I've outlived 4 laptops so far.
Sad only because these children are sleeping on concrete....