CBS was the first network to fire a show last year, axing "Smith," which had the same troubled time period as "Cane." "Smith" averaged a higher rating, but it fell off faster than "Cane" week by week.
Plus, all sorts of other factors drift into the equation, such as whether the network has anything better to punch in a slot, a show's cost and even executive pride. In all three cases, things tilt toward "Reaper" outliving "Cane." The CW doesn't want to lose a quality show; CBS doesn't want to support a show that isn't competitive in its time period.
For now, network executives are playing a cautious game of wait-and-see, thrown off balance by this season's X factor of significantly increased DVR viewing (set at 20 percent penetration and counting). The general consensus on factoring in DVR viewership is that hit shows are still hits, flops are still flops, but middle-ground/borderline cases could shift due to the additional measurement.
With both "Reaper" and "Cane" arguably borderline, upcoming DVR viewership figures may decide the fates of both.