It seems that the skewer mounted racks like the Old Man Mountain Sherpas put nearly all of the stresses due to a loaded rack directly onto the wheel rather than the bike frame. In my case I've attached the upper rack mount points using over-sized rubber hose clamps so there is very little force transmitted to those under any conditions.
You still need strong wheels of course but it seems like a lightweight frame that's not made to endure fully loaded touring stresses would do just fine with a rack like this. I've never seen this recommended so it makes me think I'm missing something.
A frame flimsy enough to actually need that kind of pampering - as opposed to simply being an easy way around there not being any eyelets - is likely to be too flexible to behave well with a rack mounted regardless of how it is attached.
