I see what you’re saying, but I don’t see this as a problem. Some of this confusion comes from the choice of “post_type” as the name, which I agree is a misnomer – really it should be “content_type”, but there’s some legacy naming at work here I presume.
So you have a bunch of content types including Post and Page. You might create another, like “Event” or “Review”.
Out of the box, WordPress lists the content of type Post (only) in the blog. That makes sense. But there’s nothing inherent about “Posts” as fas as I know that “makes them show up in the blog” – rather, when the Loop is created, only contents of type Post are queried. If you’d rather the blog included just “Reviews”, or “Reviews” AND “Events”, or any combination of content types, you can just use the query_posts functionality to change this. For example:
query_posts( array('post_type' => array( 'post', 'event', 'review') ) );
Put that before the loop, and you get all of Posts, Reviews, and Events in your blog. You can read more about it and all the options here: http://codex.wordpress.org/Function_Reference/query_posts . I believe this is a very simple way to achieve that functionality – it simply overrides the default.
From the Codex:
query_posts() can be used to control which posts show up in The Loop.
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You can customize the presentation of your blog entries by combining it with page logic (like the Conditional Tags)—all without changing any of the URLs.
So it’s not that new custom content types are inherently “like” Pages or Posts – they’re all the same really – but Posts are just the only ones queried by default.
Now, perhaps it’d be nice to build this option into the Control Panel – i.e. “Check which content types to include in your blog” – but I suppose if you’re savvy enough to be using custom content types at this point, you’re able to add a query_posts() line to your theme.
Perhaps it’ll just be a slow transition for people to wrap their heads around the expanding, and perhaps overloaded, concept of a ‘post’ in WordPress – but I think this is a great step toward making WordPress a more robust CMS for those who need it, while still keeping it simple and streamlined for the average user 
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