Microsoft rushes to fix browser after attacks; no fix for XP users

I can't answer why you would think that, but it sounds quite unlikely. If you are still using XP, you should be scared. It's not a "tactic," it's the reality of your security situation. No vendor has any financial, legal, or social interest in your safety, and on top of that, you are running on tech that lacks many modern security features that at least delay the exploitation of vulnerabilities.

As to why Microsoft would care beyond altruism and their image with XP users (hah -- this is funny because you could hardly imagine a less profitable group of people to have a good image with), I can't imagine. They don't support XP any more. It can't represent a significant ongoing cost to them any more, since they neither sell it nor offer patches, upgrades, or any other service for it.