If you read the suspension reason you'd find the complete lack of the word "bandwidth" - there are quite a few Wordpress plugins that are horribly coded and utilize way too much cpu/ram for a free service to allow them to continue stabily.
One such plugin is WPRobot, which is why it was added to the terms about 2 months ago under Auto Generated Content:
* Auto Generated Content: Sites that use scripts to automatically generate content are prohibited, this includes but is not limited to AutoBlog scripts and anything else that automatically generates websites for SEO or other purposes.
That's likely what's causing the suspension, unless it's the Site Map Generator for Google which has been known to cause it at times as well. It doesn't help that you've got some of the MultiUser stuff set up too - that's not exactly easy on performance.
For the record, high resource usage suspensions are caused by CPU and RAM, and not for short bursts - we're talking extended periods of time for a script (30-60 seconds - no script should be over a full core for that long and be allowed to continue anyways), and NOT bandwidth.