I'm sure that if the press release were being served off a domain that was even a little bit recognizable, like 'thomsonreuters.com' or similar, everybody would be willing to accept that as official. corporate-ir.net just sounds sketchy.

Also i doubt that typepad would be as trusted if your blog wasn't as popular. If it were some company whose blog i've never read before, i wouldn't be inclined to trust announcements from typepad. but everybody here knows the aws blog.