While I agree with you, have you ever tried explaining svn or git to somebody non-technical? It's not at all easy. Now try and explain to them how to commit and push files. Where does their repo live? How do they get at a file from another computer? How do they share it with somebody else?

There's value in a solution that makes copying your data to multiple systems drop dead easy and automatic, and Dropbox is in that niche. If you need more {robust|reliable|scalable|detailed} file history, it's not right for you. But you can bet there are tons of people in Dropbox who delete things a lot (just like I have met people who store "important" email in the trash folder)