Wiki's for Businesses

I ran accross this site which is commercial in nature. It allow businesses to create "secure" wikis. I checked out some of background info provided and it appears that some businesses are creating wikis to cut down on the amount of email and for project teams to collaborate on projects.

It's interesting that they feel they have to go to commercial sites since there are free wikis that offer password protection? Perhaps the security is marginal on the free sites.