Honest question: Why? I assume it's to be able to access them from anywhere with a browser and the Internet but I'm curious. Thx.
Are you curious to as why people use services like Dropbox, or why it would be nicer to have it incorporated in iCloud than having to use an additional service for it?
Right now, I'm using backup, calendars, contacts, e-mail, notes, reminders and all the contents in a certain folder with the cloud. The folder syncing is the only service not included in iCloud.
Having it all under one roof, with one password, would be nice. If they'd incorporate say SugarSync into iCloud - I'd be happy. And probably many with me, because it's a well used service and I'm not the only one who likes having all the cloud services under one roof
As an example, I dropped Evernote the second I realized how the syncing of notes worked in iCloud.