I used to work at Google. I didn't study for the interviews, I just showed up. It went well enough to be hired. I did study CS and know my algorithms and data structures though.
Other people do though.
Perhaps you are one of those people who could just walk in and Ace the final exam for an intermediate data structures and algorithms class taught at colleges.
And finally, it would be fascinating to plot career performance at Google vs time spent interviewing. Intuitively I would expect those who got an offer without studying to do better (higher latent intelligence), but I could also see it going the other way (lots of studying correlates with willingness to work hard on boring problems, which is what most Google engineers actually have to do day-to-day).