drmike: No, wp-cron would not check for future posts unless they were made. The scheduler for future posts is a one-time event that's scheduled for the time of the post itself, and it's scheduled when the post is made.
Terryphi: You need to change your .htaccess so as to allow that wp-cron hit to go through.
Wordpress activates wp-cron whenever it thinks that there is a scheduled event it needs to process. That scheduled event could be anything. In your case, it's probably wanting to process pings and MIME type checking for a post you made. It will do that for every post, that's normal.
By blocking the call to wp-cron, you're preventing this from happening, and so it will try to do it every single time somebody hits your page. The only way it will ever stop is if you allow it to actually happen and thus allow it to do its job.
Wordpress runs wp-cron as an external webrequest so that it will process the cron stuff in the background, and not in the foreground while the reader waits for it to run.
There are several reasons that Wordpress runs wp-cron, and yes, it is critical. You cannot block it (for very long anyway) without breaking some things.
Terryphi
modifoo
geofones