This card can be seen as the spiritual successor to the "Blue-Eyes White Dragon". Both are used by one of the best Duelist in their respective series, and both have a final fused form that requires three copies to Summon.
Based on this belief, the ATK and DEF of "Cyber Dragon" are both exactly 900 points less than "Blue-Eyes White Dragon".
Referring to above, in fact, some fans who bought the Cybernetic Revolution packs mistook "Cyber End Dragon" for a possible version of "Blue-Eyes Ultimate Dragon" under the effects of "Metalmorph".
Fusion evolutions of "Cyber Dragons" share a pattern for their DEF. The DEF of the Fusion Monster is equal to the original ATK of the monster just below it in the evolution chain. For example, "Cyber Twin Dragon" has the DEF of 2100, identical to this card's original ATK, and "Cyber End Dragon" has the DEF of 2800 which is the original ATK of "Cyber Twin Dragon".