Note that Hitachi did offer 24VDC Source Voltage -  only as a special order option (which Reliance chose for the 45C903, 45C905, and 45C907).

As indicated in the tables above, Reliance Electric:

• did not offer (re-label) the 64 I/O unit.
• did offer 115VAC Input as a standard model.

CONCLUSION:  

• Reliance Electric chose units from Hitachi (available as an option - only in large quantities), based on the needs¹ of their U.S. customer base.  In other words, Reliance re-labeled only the "HR" units, not the "HRP" units, in the DC models.
• Hitachi additionally offered E-Series which had "Positive Logic^(*)" ( PNP transistor ) units (as opposed to "Negative Logic" (NPN transistor) units.
• To replace a Reliance Shark X (models 45C903, 45C905, or 45C907) with a Hitachi E, 115VAC had to be provided for the power to the unit.
• When replacing the 45C904, 45C906,  or 45C908, Input devices (such as photo-switches, inductive proximity switches, etc.) that were rated for 115VAC had to be replaced by devices rated for 24VDC.

Footnotes

(*) The letter "P" was added as a suffix to the part number (i.e. E-20HRP) to identify these Positive Logic devices. The difference between these two are more commonly known in the U.S. as "sinking & sourcing ²".

¹: Referring to the preference of the time (Circa early 1990's) toward "Sourcing" Field Inputs. Since that time, perhaps due in part to globalization, perhaps due in part to the influx of OEM equipment from the Pacific Rim and from Europe, we have seen an almost complete reversal in this mindset.

²: If a device provides current (to the PLC) when it is ON, it is said to be  sourcing current.  Conversely, if a device receives current when it is ON, it is said to be  sinking current.    There are both sinking and sourcing  field devices, as well as sinking and sourcing input modules.   PLC users in the U.S. have historically preferred "Sourcing" field inputs.  Elsewhere in the world, "Sinking" inputs is preferred.