It seems almost inevitable that software projects become more complicated over time. Unless simplicity is a core requirement, complex features are constantly added to popular software (and rarely removed). By trying to solve a wide variety of problems, the number of options and screens must correspondingly increase. I'm really impressed by new approaches like Posterous that challenge the way blogging has been done in the past. It's these kinds of approaches that can lead to software that can be either as simple or as complex as the user needs them to be.
I agree, Posterous is awesome. It would be even more awesome if you could somehow just embed a little code on your own template in order to display your blog on your own design.
As far as I know, you currently have to learn the platform (Wordpress, MovableType, etc) in order to make a custom design. I feel like there needs to be a way to have the blog fit into the design without having to code your own CMS.
They haven't been around very long, I wouldn't be surprised if they figure out a slick way to address those problems in the future. I'll be interested to see how they approach it if they do.
