Flash datasheet information, why two input high levels?
The normal logic inputs are recognized as a logic 1 if the voltage is above Vih (2.0 volts).
However, CMOS devices often take current from the supply if the input level is not close to the supply rail.
The level at which they specify the standby current when using CMOS level inputs is 100uA(Isb2), but to guarantee that the CE needs to be at Vdd-0.3v.
If you are only using TTL inputs that reach 2.0V they only guarantee 3mA (Isb1).
The device will function correctly logically with either, it is just the standby current that will differ.