It's hard to imagine the original Dead Rising game warranting an R18+ rating, in spite of the similar levels of gore.
The game has taken a turn for the dark and gritty, sporting a new next-gen brown look which is sure to change the tone of the violence somewhat.
Gone are the brightly-lit environments and wacky weapons in favour of something closer to Resident Evil meets Gears of War.
Regardless, examples so far have shown that the Australian Classification Board is far more likely to look upon a game's technical levels of gore than the game's tone.
Where characters are realistic and blood is present (even if it's zombie blood), the gore is treated as having the highest of impact, with little consideration paid to the notion that excessive gore can reduce or even mute the violence.
That said, there is little about the new Dead Rising 3 that would deter someone from slapping it with an adults only rating. It's just interesting to note the comparison.