I'm sure lots of people have that question, but apparently no one has the answer you're looking for. I have version 3.5.5, but I'm not even sure what you're talking about - is there some kind of tab that shows the most viewed videos, or are you talking about actually typing 'most viewed' into the Search bar? If the latter, I do get results when I type in that criteria - it would seem a major miss for them to not return any results for that particular query, and you should just file a bug with Google about it.
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