I've been around and deeply involved in video gaming for almost my entire life. I've worked for gamestop and IGN in the past and am well versed in in the different games around. My all time favorite video game series is Mortla Kombat, and I've found a few irritating errors in your posting about this game.
First of all this game is titled Mortal Kombat. Not Mortal Kombat 9, not mk9, not mk8 (which would be more accurate due to the fact that MK vs DC was not cannon). Technically this is the 9th entirely new game (1, 2, 3, 4, 5 deadly alliance, 6 deception, 7 Armageddon, 8 vs DC, 9 Mortal Kombat) However, many view Ultimate Mk3 as it's own game as it was released on Arcade. MK Trilogy and Mk Gold were also big games and can almost be counted, and since MK vs DC isn't cannon it's hard to really say which MK this one is.
Secondly, this MK is not a reboot. It's a continuation following the events of MK armageddon. Halo 2 and Halo 3 were not reboots, which came out YEARS after one another. It's been just 2.5 years since MK vs DC, and just 4.5 years since Armageddon.
Callig a game a reboot implies the game has been MIA for years and clearly MK has not.