Yes, you are correct, the Carrera is not available with PDCC. And the reason they went down to a 3.4 was mainly for efficiency purposes, and a 3.6 liter engine just wasn't necessary for adequate power. The reason the 3.8 remained was because it was perfect for making 400hp. 

And about the press release, the people who write them aren't engineers or test drivers. Usually they're with marketing, and use a lot of filler words to get their point across, and sometimes even make typos. I've seen one press release mention a GT2 RS 4.0! 

I'm not saying the people who write them are idiots at all, because I enjoy every single one of them and think the writers make the products come across very well.

I acknowledge what you say Porsche said on their site, and trust me, the engineers didn't write that, it was probably some marketing person using filler words.

Downsizing is for maximum efficiency.