Ryan, that's a great observation and I totally agree with you. I don't know the location for that sounding, but when this event was pending I noticed a couple different NAM reads for 3 km MLCAPE of 75 J/kg in Missouri. One run placed a sort of bullseye northwest of St. Louis, and a later run depicted a narrow strip extending through central MO out of Arkansas. (I ran a RAOB sounding that I wish I had saved, which showed a nice, fat low-level CAPE profile.) I believe there was an even higher value down in LA or AR. The two central MO storms, including the Rolla EF3, coincided with that strip, which presumably moved east and provided the necessary low-level energy.
I think 3 km MLCAPE is a valuable tool for winter and cold core setups; I believe that's something I got out of Davies' article when I read it (it's been a while), and NYE certainly bears it out. I've also been paying attention to normalized CAPE as an overall indicator of parcel acceleration, and suppose that by its definition it would apply to low-topped storms as well as to typical, higher-topped convection.
All that being said, some of the storms the other day went tornadic in environments that had some pretty skinny, stretched-out CAPE. But maybe there was something I missed; I just remember being surprised when I looked at some soundings.