I'm not sure you can say that we've decided to abide by the GPL - that would suggest that we were in contravention of it before. There are many folk arguing on both sides of this.

However, the view within the WordPress community is that a theme should be GPL. It's not actually important whether the community is right or wrong - if we want to be a part of a community that feels strongly about something then it's important for us to share those values. And that's why we've decided to apply the GPL to our themes.

I'm not convinced it's going to bring us riches - it didn't appear to work for Brian Gardner and although his themes are GPL now, they're no longer freely available. This appears to have caused repercussions - I see that his work is no longer promoted by WordPress.org - so it's clear that if you want the support of the community it's important to make all your themes freely available and stick to a service based offering for the chargeable element. Whether that's viable for smaller businesses, I don't know. Guess we'll find out :-)