How in the world can this be considered reasonable for them to track you across other apps and sites? This like if the local grocery store owner would install hidden cameras to spy on me at home and at work and in the car and one day somebody forced them to ask if I'm sure that's what I want them to do. This all makes me start feeling like I might finally want an iPhone...
The more accurate analogy would be the grocery store owner teaming up with other local businesses to aggregate your shopping habits across stores into a central database. What you're describing would be if facebook installed a RAT on your computer after visiting it.