H2FC: No worries, mate.
As for the reason why people pay for some themes, well, there are some reasons.
A lot of free themes will have links in them, often in places you won't notice, for the theme designers projects that they're attempting to get some offsite
SEO linkage for. Name the theme to your niche, people in that niche will use it, all of a sudden you're getting links from a site that's not known to be one of your own, but is in the same niche space, and major SEs will give you some link juice for it.
Conversely, the paid for themes will often have their own internal
SEO elements to help you boost your own sites rankings (i.e. related posts internal links, optimised ping codes, etc.) and will often be more modular, meaning you can even change the layout of the blog easily enough.
The
Thesis theme is probably the best example of why you'd actually wantto pay for a Wordpress theme. It's almost limitless in it's customization capabilities, and is
very Search Engine friendly.
Bookmarks