Somebody mentioned that the Nords and other residents of Markath still sleep in the ancient stone Dwemer beds (there are some in the inn and in Understone Keep, for instance).
If they are big enough for other races to sleep in and not go looking for a more suitable substitute, then either the Dwemer were about the same size as the other races or else they deliberately and consistently made beds that were oversized for members of their own race.
Unless they just liked bigger beds so they could fit more Dwemer in them, because there ain't no party like a Deep Elf party, amirite or amirite?