It does not say that at all, in fact it says:
"The upcoming version of Mac OS X, Mountain Lion, will reportedly include warning messages that strongly discourage users from installing apps from sources other than the Mac App Store. Fortunately, it will be possible to turn this off in Mountain Lion and install apps from anywhere you want, but Apple is continuing down the dangerous road of making their products less open."
"Strongly Discourage" != "Disallow"