Some of the information posted above is not correct, it’s based on using everyday senses of terms like “independent” rather than the specific mathematical/probabilistic meanings, or using definitions from websites that aren’t completely accurate (or just plain misunderstanding the concepts).
In fact, this is correct:
Yes, as @menloparkmom says, the decisions are made independently (i.e., separately) by different committees – but that does not make them independent in the probabilistic sense.
Here’s a thought experiment that may help clarify things. Person A applied to a bunch of schools; they got accepted to Stanford; do you think they got accepted to any of the other schools they applied to? Any person not being obtuse would say yes, they probably got accepted to most if not all of the other schools. But if all those admissions events were independent, you couldn’t say that, the fact that they got into Stanford would say absolutely nothing about those other schools.
Maybe a better way to think about it is to use correlation. One way to think of correlation mathematically is that it’s a value between 0 and 1, relating two events/sets of data; if the value is 0, then they’re totally unrelated – independent; if it’s 1, then they’re perfectly correlated. Any non-0 value means they’re dependent – in particular, they don’t have to be perfectly correlated to be dependent.
Most likely the correlation between admissions decisions at schools is fairly strong, especially if the schools are similar (like top schools are). Not independent, not perfectly correlated, but still related, and hence dependent.
Getting back to the OP’s original question, i.e., will one’s chances of getting into at least one top school be greater if they apply to more?, the answer is basically yes. Think of it this way, basically dividing applicants into three groups: some have basically no shot to get into any of the top schools; some are likely to get into more than one of them; others have a shot at some of them. For people in this latter group, applying to more than one of the top schools would increase their chances of getting into at least one of them.
But should you do it? That depends. You should first evaluate other considerations, like fit and affordability. You should also make sure to include sufficient match/safety schools on your list. And you don’t want to apply to too many schools, so you have sufficient time and energy to do a good job on all of them.
After that, if you still want to shoot for some top schools, you should try to assess your chances at such schools, you might be able to get some idea where you’d have a better shot. Maybe you can find some where your chances are increased, based on “institutional priorities”, or whatever. But remember that any increased chances of getting into these top schools will be marginal, so you need to make sure you’re taking these other steps, to have a good list of schools to apply to.