It's quite possible to host a "normal" WP installation with custom themes and plugins on WordPress.com (on the more expensive plan), I've done it a few times. But as much as I want to like it, I can't wholeheartedly recommend it. Some stuff that should be easy is just ridiculously difficult, like pulling logs programmatically. I think the main audience it caters to is people hosting a basic site with off the shelf themes.