[Daniel14]

Sorry for not specifying that, thanks for the correction. The exception to promoting being legal of course is, when the product in question has a monopoly on the market. However, I doubt that's the case with Google Search. Again, IANAL, but a) the barriers to enter the industry are pretty small, b) there are plenty of alternatives, c) you can switch to them extremely easy, and d) Google would go out of business if they tried raising prices (i.e., they don't control the market).

Also, my point still stands - Google has been promoting other products on their homepage for a long time without getting sued. I don't understand how Plus would be different from, say, Reader.