It requires extra math that users shouldn't be burdoned with. Why should I have to pull out a callendar to figure out how many
days until my target date when the wallet can do it so easilly? Same with blocks, the math may be simpler but still unnecessary.
I personally decide the amount and duration of my term deposits using the interest calculator @
http://hodlcoin.github.io/ and a calendar before I do anything in my wallet so I guess I don't see the purpose of those features for myself, but I'm sure it would make things easier for others who use just the wallet.