I'm going to save you from a WordPress.com/forums pile on.
It's understandable that you think the lack of css editing capability is lame. As someone who has worked as a professional web designer and web applications developer, I fully understand the innate desire of the programmer to tinker with anything, be it a program, a website or a template.
That being said, there are several good reasons why CSS and XHTML aren't editable on WordPress.com blogs, all of which have been discussed ad naseum on this forum:
(1) First and foremost, security. Anything editable creates the risk of exploitation, and there have been several high profile examples of similar sites being exposed to such exploitation, including Livejournal and MySpace. Yes, Blogger lets you edit templates without fear of security risk, but Blogger works differently from WordPress, which directly executes PHP on every page view.
(4) Have you seen the quality of the templates and themes on other free, hosted sites? Take Yahoo! 360 for example - the templates are nowhere near as professional and sleek as the ones currently offered on WordPress.com.
(3) There is something to be said for not being able to edit your HTML and CSS; it forces you to focus on content rather than presentation. For many, this is a plus. On past blogs, I know that I have become so caught up in creating and tweaking themes that my blog became less about communication that about presentation.
(4) Even if you do not want to pay for webhosting, you have other options if you want a custom template. As explained in (3), there are other potential bloggers that do not. And remember, it is a free service.
The bottom line is that WordPress.com is focused on communication and broad usability. Custom CSS, as you have implied, is not critical functionality for a blog. Communication and usability, however, are critical. And WordPress.com probably provides these functions more aptly than any other free, hosted weblog service.
Please don't take this as a rant, I've just seen people ripped to shreds on these forums for insinuating that the service is deficient, and I wanted to give a good, logical explanation before the ad hominem attacks started flying.
Oh, but I don't work for WordPress or anything, so maybe the squeaky wheel gets the grease.