People love Google services, but they don't like the very things that make those services great. Without knowing who you are and what you're about, they can't accurately filter spam or show you relevant results/ads. There are other spam filters, but they don't work as well because they don't know you.
Yes, Chrome sends information back to Google just like Google Search does: it tracks what searches you make through the Omnibar. Firefox does the same thing when you make Google searches in their search box.
Filtering spam has nothing to do with my search queries. It's all about finding duplicate or nearly duplicate messages sent to many people at once, all one needs is a large sample database.
Which is when you get false positives, about the worst thing a spam filter can do. Millions of legitimate organizations send billions of duplicate messages per week. And what's spam for you might not be spam in my eyes. Or maybe it's just a case of needing to unsubscribe from the mailing list. Maybe there's a phishing message and a legitimate message coming in at the same time. Your spam filter needs to know which one is which, it needs to be quick to react to new developments, and it needs to know what you want to see and what you don't.
Spam filtering is hard. Gmail got popular because of their space and their nearly bullet-proof spam detection. If it was easy, someone else would have done it.
Yes, Chrome sends information back to Google just like Google Search does: it tracks what searches you make through the Omnibar. Firefox does the same thing when you make Google searches in their search box.