They manage to sort out aliased domains sometimes, but it can take between several years and never for it to happen, having a permanent redirect from the aliased domains to the main name does ensure that it happens sooner rather eventually.
That possibly does account for the sudden drop since the "Panda" update.
The general drop off in people actually visiting forums, may be due in some part to the gradual but ever increasing use of RSS feed readers and websites that republish RSS feeds.
After all you only need to read some things once, and unless you are inclined to comment or answer the post you need never to visit the originating page.
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Chris.
So long, and thanks for all the fish.
http://webmaster-talk.eu/