1. 74ls series haven't z-state for TTL, only "0" or"1". On the not connected input you have 1 (for ls series).

74LS244 et al.

 

74LS244 et al.

I think the TS meant, that they don't have a way of detecting a Hi-Z output connected to the probe. You can do it, but it takes some work an ingenuity.

 

74LS244 et al.

I know. I mean that 74ls00 and 74als00 don't have an undefined state, and they can't show no signal at the input. Only 1 or 0.
Tested experimentally in practice. Only 7400 standart series can do it.
Don't believe me? Try it yourself. And write to me.