The fact that I got all this input overnight is in itself a good argument.
I intentionally omitted what I already did in the meeting to defend PW, and it's nice to see other people mentioning the same things:
Told my personal experience, not being a backend coder, I have built my personal site completely from scratch and didn't get stuck even once;
After my experience, brought PW to my engineering department, asked them to build one of our client's site with PW and got such good input that it's now our dev platform for small to medium projects (cases such as Volvo's CRM we use our own platform);
Showed him hands on how easy it is to make changes to my own website, added a field to my portfolio section, customized it and had it output on the frontend (under 5mins);
Demonstrated that PW doesn't make any assumptions whatsoever as to what you're going to build, being a blog, products catalogue, news magazine, etc;
Mentioned that it's been around for 7 years (is it?) with regular updates and we have a new major update coming this week;
Explained the learning curve: any programmer that picks up PW will be building a website the next day.
Still, great extra arguments here. I owe you guys a beer!