Comcast's technical side does a lot of interesting work: they were one of the first big ISPs to roll out IPv6, for instance. Not saying they're on the whole a benevolent (or even trustworthy) corporation, but these sorts of things don't need to warrant immediate suspicion.

Now that they know they can charge extra for it, they decided to make the investment.

No, it's just some incremental improvement. Anyone forwarding traffic needs some kind of congestion control system. This is just another implementation of it.