Thing is, I don't consider it a small feature! Until this is added personally I don't think Tablo is ready for mass-market.
With all the daily shows that are recorded by various family members, two weeks worth of programming would fill up the Tablo disk, bumping the other "more important" unwatched shows. I don't want to have to remember to log in and mark those non-daily shows as protected if I haven't caught up yet. More importantly I would have a riot on my hands in the household and cries of "Dad why did we turn off the FIOS tv???"
To me Tablo (and DVRs in general) is about automation: setting it and forgetting it until you want to watch it. If you have to go in and manage recording by deleting then it defeats the purpose of set and forget.
FWIW, I pay around $100 for "cable".