As dgillz pointed out, the toolbar is an OPTIONAL download. Which means if someone installed the popup blocker, it's because they don't want to see popups. Plain and simple, the users that have this tool don't care who the advertisers are or what they're selling, they don't want to see it. I've been using it since it came out, and I can't recall seeing a Google popup. The popup blocker doesn't stop banner ads on web sites, so there is still a means of (less intrusive) advertisement available.
I signed up on the national Telemarketer "Do not call" registry because I do not want to be bothered. I have Spam filters because I do not want to be bothered. I have the Google popup blocker for the same reason, and if popups start getting through (even Google's) then I will find another blocker. I'm tired of everyone throwing their products, their services, and whatever else they think I "need" in my face. If I want your service I'll come to you, until then leave me alone. And no article, lawyer, or EULA is going to change my mind.
I have the right NOT to be harassed, and the Google popup blocker is helping me stop the harassment. The telemarketers screamed when the US Government started the "Do Not Call" list earlier this year, but when 23,000,000 people signed up the first week, there wasn't a whole lot they could argue about. Even when the judge in California tried to stop it, there were over 50,000,000 people signed up on it and there wasn't much he could do about it. "50 million people can't be wrong."
What this article(complaint letter) boils down do is the fact that some advertiser has realized that he can no longer "force feed" his products/services to us and that we now have a choice as to whether or not we have to see it. Bottom line, they're scared because Google provides a means to stop their harassment and they're trying to find a way to shut down Google's popup (harassment) blocker.
Hope This Helps!
Ecobb
"Alright Brain, you don't like me, and I don't like you. But lets just do this, and I can get back to killing you with beer." - Homer Simpson