I agree with you, benefit of installing arbitrary software does exist -- but that benefit alone doesn't justify the significant "openness" hype around the platform. The article points out the many ways in which you are not in control of your device.
That's what I find most compelling about the Android platform. As long as I have access to the Android Market and the ability to install apps directly from the internet, most of the problems mentioned in the article can be sidestepped. With that being said, I do find the trend mentioned in the article to be somewhat alarming. Removing those two features really cripples the phone, but I expect most Android phones to leave those enabled.
(I'm a bit stricter with stability on a device like my phone, else I'd try the RCs.)