It is important to note that Wordpress.com and Wordpress.org are separate entities. The differences are explained in detail here. Basically:

WordPress.com is owned by a privately held company called Automattic.

You have to understand a little bit of history of the open-source WordPress project to understand Automattic's contributions and the reasons why they get favorable treatment such as the ability to use the WordPress trademark and the coveted WordPress.com domain as part of their paid product.

Automattic was started by the co-founding developer of the open source WordPress software, Matt Mullenweg.

Matt created Automattic in 2005, almost two years after WordPress, with the primary purpose to make WordPress hosting easier and allow people with little technical knowledge to start a blog with WordPress.

Since WordPress.com platform was powered by the open source WordPress software, Automattic had a vested interest in the further development of the free WordPress software.

Several of the early Automattic employees were contributing developers of WordPress prior to the company, so it should go without saying that financial interest wasn't the only reason why Automattic invested in WordPress.

Because the open-source project didn't really make any money in the beginning, Matt first registered the WordPress trademark through Automattic.

As WordPress grew in popularity, Automattic donated the WordPress trademark to the WordPress Foundation in 2010 to ensure long-term sustainability of the non-profit project.

It's important to note that Matt Mullenweg is the CEO of Automattic and also serves in the board of the WordPress foundation.