It all depends on what/why you ride. I could be quite happy owning just one bike (I have a 'one bike') and it wouldn't limit my riding too much, the other 3 or 4 that I'd rather not be without are just a luxury / choice.
1 rigid 29er with ss-ability and wide-range handling like my Jones
1 road bike like my Equilibrum
and ideally a town-hack SS
..would do it all apart from the odd Alpine chairlift trip.