Yeah, what you probably won't ever get on the NASA site is a page that contains blatant untruths that someone knowingly put up as a joke or to discredit something they don't like. However, I think you would have to be unlucky to actually see that on Wikipedia, since any page with a controversial subject is likely to have a dedicated editor who will quickly revert any malicious changes. And more subtle systematic errors would be difficult to perpetrate because they would likely be picked up and corrected before long.
On the other hand, the people who write the NASA articles are exactly the same people who are likely to also add their latest research to Wikipedia. The difference being that once a page is "published" on any non-Wikipedia site it could be difficult to correct any errors due to the publication process that the site requires - the author is probably several steps removed from the website technician who actually makes changes to the site. Whereas errors or research updates can be made immediately to Wikipedia pages.
So, in my opinion, the risk of falling foul of a deliberate error on Wikipedia is far less than the risk of seeing an inadvertant error or outdated research on a NASA page.
I do agree that you would be very unlucky to fall foul of that on Wikipedia, and honestly I don't know how website editing is handled so I'm sure you're right about more small errors slipping through - still a small error in spelling or grammar doesn't make the actual content of a webpage unreliable, and I don't feel like errors in content would be made on Nasa's website. In regards to webpages being outdated, I'm sure new ones in the research area would be published eventually to keep up with the times - though clearly in this example the article is outdated as there has yet to be a response to their critism. This doesn't mean to say that their original article was full of crap however, scientists often try to discredit each other due to their own egos and that they think they can make themselves look clever by crapping over other peoples' hard work. As I said scientific research articles do fall under a great deal of scrutiny; it would seem counterintuitive for a research body to put that much care into its articles and yet let its webpage slide, it would also turn them into a joke of the science community if they did.
I still stand by my assertion that Nasa would be more reliable for content than wikipedia - but only by a smidge. They're both quite reliable in my book. If I'd had known this was going to turn into such a debate I wouldn't have been so glib in my first response, I even voted for Wikipedia for irony's sake - I guess there's egg on my face now! Without looking at the original article I can't be sure how sensationalist Nasa's claims were, but "Science" where the article was published is the leading scientific journal in the world - most researchers would give their right arm to get an article in there so I doubt what they wrote on the webpage was that misleading if it's based primarily on the article.