Reaction of nitro compounds with strong alkali?
In order for a compound to act as an acid, it must have a proton which can be abstracted. As you correctly pointed out, tertiary nitro compounds have no $\alpha$ hydrogens and therefore they cannot be deprotonated at the $\alpha$ position. 

Of course, they could be deprotonated elsewhere, but if the other groups are just alkyl groups then this isn't really feasible as they have such a high $\mathrm{p}K_\mathrm{a}$.