Hey, that's not a stupid question! It's quite valid. First of all, do you have a 61 key T5 or the 76 key version? I only ask to get an idea of what "more keys" would mean to you.
Right off the bat, some Classical music requires a full 88-note piano keyboard, so that's one place where people want more keys.
Beyond that, while 61 keys is plenty for most music, and I play mainly on a 61-key model, there are cases where some extra keys would be useful. When I play Chariots of Fire, for example, I like hitting some deep bass notes when I do play it on a regular piano. And then there is the last verse, where the melody is played one octave higher than at previous points in the song. That puts it as high as the Db right above the highest note on my 61-note keyboard, so I have to alter my arrangement when playing on that keyboard, versus playing on an 88-key piano.
Upon taking a closer look at the 76-note keyboard of something like the Genos, I see that this also would be enough keys to play Chariots of Fire the way I like. So, yes, 76 keys is enough for most music we would normally play. But again, some Classical music may require the full 88. Perhaps some other complex music, like certain jazz tracks, would also benefit from the extra keys, as well.