Agreed, but the problem is more complex I think.
To start with, Wikipedia doesn't allow for debate within the article. Most knowledge in soft sciences is controversial and will remain so. A good Wikipedia article that deals for instance with "user experience" might have to be written as "user experience (1)", "user experience (2)", etc. Each of these chapters would have to be signed by its authors since the first thing an academic does when reading something on the web is finding out who (i.e. what kind of global frameworkd) is behind.
Academics need recognition, Wikipedia should come up with a scoring system that could identify contributions (something like "A" wrote about 30% of a really cool introduction and he also wrote the first draft). So its about signing again.
Now *my* *main* argument against doing something in Wikipedia (I am an academic): I want a wiki to be place where anything goes. Crazy ideas, new ideas, unfinished stuff, biased tutorials, etc. For half-serious papers we got conferences and various academic peer-controlled wikis or other CMS and for serious ones journals. Wikipedia can't (and should not) be used as place where I can do notetaking, explore ideas, write tutorials that fit *my* requirements, have students writing, etc.. So I got my own wiki and since my own wiki is there, I'd rather add "encyclopedia-like" pieces to my own. Makes it an integrated whole. In addition, most of my pages show up very high (much too high actually) in google search. I.e. I can actually sell this as minor contribution to the world in my CV.
After working on my own wiki, there is just no time left for Wikipedia. Other academics also produce a lot of open contents and in a different way than I do, but they probably have the same reaction: An Encylopedia like Wikipedia is cool and useful but it's not a fun medium and it does not cover our most important needs, i.e. be some sorte of public external hard disk where everything but serious publications could go ...
Finally, there is wikibooks and the agonizing wikiversity. Wikibooks seem to me a good place to contribute. And there you can see some more academics I think.